Rocks and Minerals

Rocks and Minerals asks you to do two things quickly and correctly. First, identify a specimen from what you can observe: its hardness, streak, luster, cleavage, density and reaction to acid. Second, explain what that specimen tells you about how it formed and what happened to the Earth around it. The first skill is a toolkit, a short sequence of tests you run the same way every time. The second is a model of the rock cycle: magma cools, sediment is buried and cemented, and rock that is heated and squeezed changes without melting. Strong teams keep both in view. A correct name with no explanation of formation loses the reasoning points, and a convincing story attached to the wrong name loses the identification points.

Identification is worth at least 30% and at most 50% of the points, so the rest of the test is classification, data and explanation. The scope below follows the 2027 rules manual for Divisions B and C and the 2027 National Rocks and Minerals List, which is the same for both divisions. Divisions B and C share most of the topic outline. Division C adds several items (solid solutions, phase diagrams, silicate structures, crystal systems, the evolution of igneous melts, metamorphic facies and thin sections), and anything limited to State and National tournaments is marked in the text.

Event format

If the event runs as stations, the supervisor sets and announces the time at each station. You cannot go back to a station, but you may revise your answers while you are at later stations. The only material that may leave the binder is the National List.

What the rules cover

The table summarizes the 2027 rules manual (Rocks and Minerals B, rules 3.h–3.i, and Rocks and Minerals C, rules 3.h–3.i) in plain words. Check the manual on soinc.org for the exact wording.

Several lists in the 2027 rules are closed ("limited to"): the other properties, the habits, the igneous formations, the sedimentary textures, the index minerals, the gem varieties, the solid-solution groups and the thin-section minerals. A test that sticks to the rules will not go beyond them, so learn every item on each closed list rather than extra examples. The list of depositional environments is open, so other environments can appear.

The 2027 National List

Identification is limited to specimens on the 2027 National Rocks and Minerals List, although other rocks and minerals can be used to illustrate a concept. Read the list early and annotate your copy: it is one of the three references you may bring, and it is the only thing you may pull out of your binder at a station. A few features of the list change how you study:

• Starred specimens are identified only at State and National tournaments. Among the minerals these include magnesite, rhodochrosite, siderite, pyrolusite, rutile, zincite, turquoise, pyromorphite, vanadinite, bornite, stibnite, actinolite, tremolite, apophyllite, chrysocolla, dioptase, lepidolite, prehnite, rhodonite, spodumene, jasper, smoky quartz, tiger's eye, stilbite, willemite, wollastonite and zircon. Among the rocks they include syenite, tuff, tuff breccia, diatomite, greywacke, amphibolite, talc schist (soapstone) and serpentinite.
• Specimens with supplied information. For magnesite, bornite, willemite, syenite, tuff, tuff breccia and diatomite, the supervisor will give extra information (diagnostic properties, a formula, grain size or composition) to make identification possible. Your job is to match that information to the name, so keep a binder line for each.
• Naming conventions. The pink or tan potassium feldspar is answered as "Orthoclase/Microcline" or "potassium feldspar"; the rules also note that white or pink/tan orthoclase/microcline occurs in granite. Tourmaline is accepted for the whole group. Celestite may also be called celestine. Goethite/limonite and agate/chalcedony are each one answer. Rock salt and halite, and rock gypsum and gypsum, do not have to be told apart.
• Classification quirks. Bauxite is listed as a sedimentary rock, not a mineral. Opal sits among the quartz varieties even though it is an amorphous mineraloid. Grossular garnet is the green variety. Gypsum appears as three varieties: alabaster (massive), satin spar (fibrous) and selenite (crystalline).

Mineral identification

The 2027 rules open the mineral topics with a definition: a mineral is a naturally occurring, inorganic solid with a definite chemical composition and a crystalline (ordered internal atomic) structure. Each word rules something out. Synthetic gems fail "naturally occurring"; amber and pearl fail "inorganic"; water fails "solid"; obsidian and opal fail "crystalline" (they are amorphous mineraloids). That is why amber and pearl appear in the rules only as gem varieties, and why opal is a mineraloid even though the National List files it with the quartz varieties.

Composition and structure determine every property the event tests, so you can reason from one to the other. Chemical bonds set the hardness, the atomic planes set the cleavage, and the elements present set the density and some colors.

The test sequence

Run the same tests in the same order on every specimen. Consistency matters more than speed, and it makes your binder notes easier to read later. You may bring only a magnifier, so at a tournament you mostly observe luster, color, cleavage, habit and heft yourself; streak, hardness, magnetism and acid results are often given on a card or in the question. Practice the full sequence at home so you know what each result means when it is handed to you.

The rules say hydrochloric acid will not be used or provided and that a taste test is not allowed. Acid reactions therefore appear as written descriptions. Learn what the reactions mean, not how to perform them.

Hardness and the Mohs scale

Hardness is resistance to scratching. The Mohs scale ranks ten reference minerals from softest to hardest. It is ordinal: the steps are not equal, and the difference between corundum (9) and diamond (10) is far bigger than between talc (1) and gypsum (2).

Everyday tools give useful anchors: a fingernail scratches minerals of about 2.5 or less, a copper coin about 3, a steel nail about 5.5, and window glass about 5.5 to 6. A porcelain streak plate is about 6.5 to 7. Test on a fresh surface; weathered crusts and grit give false readings.

Streak, cleavage and fracture

Streak is the color of the mineral's powder. It is more reliable than the bulk color because impurities and surface coatings are removed. Hematite leaves a red-brown streak even though many hematite specimens look black or silver. Pyrite leaves a greenish-black streak while its surface is brassy yellow, which is one reason it is often mistaken for gold (gold leaves a yellow streak).

Cleavage is the tendency to break along smooth planes where atomic bonds are weakest. The number of cleavage directions and the angles between them identify many minerals:

Cleavage faces are flat, shiny and repeat across pieces of the same mineral. Crystal faces are the external shape a mineral grew with, which is the habit. Do not call a crystal form cleavage, and do not call a cleavage plane a crystal face.

Density and specific gravity

Specific gravity (SG) is the density of a mineral divided by the density of water. Because water is 1 g/cm³, SG and density have the same number, but SG has no unit.

Typical values to know: quartz about 2.65, pyrite about 5, galena about 7.5, gold about 19.3. Rocks such as pumice are unusually light because they are full of gas bubbles, which is why heft is a rock clue too.

Diaphaneity, tenacity and other properties

Diaphaneity is how much light passes through: transparent (you can read through it, as with rock crystal), translucent (light passes but the image is blurred, as with many agates) or opaque (no light, as with galena). Tenacity is how the mineral responds to force. Most silicates and carbonates are brittle and shatter. Native metals such as gold, silver and copper are malleable (they flatten) and sectile (a knife shaves them). Mica sheets are elastic (they spring back when bent), while selenite gypsum and talc are flexible but stay bent.

The manual limits "other properties" to eight, so each is worth one memorized example:

Fluorescence is not the same as phosphorescence, which keeps glowing after the light is removed, and not every sample of a mineral fluoresces, because the glow depends on trace activator ions.

Mineral habit

Habit is the typical shape of a crystal or crystal group as it grew. It is a property of the outside of the specimen, not of how it breaks. The manual lists a fixed set of habit terms; the table groups them by what you would see.

Chemistry, groups and polymorphs

The rules ask you to classify minerals into families by composition, following the headings of the National List: borates, carbonates, native elements, halides, oxides and hydroxides, phosphates, sulfates, sulfides and silicates. The family is set by the anion group: CO₃²⁻ for carbonates, SO₄²⁻ for sulfates, S²⁻ for sulfides, O²⁻ or OH⁻ for oxides and hydroxides, a halogen for halides, and the SiO₄ tetrahedron for silicates. A mineral group (feldspar, garnet, tourmaline, mica, pyroxene, amphibole, apatite) is a set of minerals with the same structure and related chemistry, so members share properties such as cleavage angles and crystal shape.

Most rock-forming minerals are silicates. How their SiO₄ tetrahedra link determines the mineral group and its cleavage. Division C must know the six structures below; the silicon-to-oxygen ratio is the quickest way to tell them apart in a question.

Single-chain silicates (pyroxene) and ring silicates share a 1 : 3 ratio, and archived tests do ask which silicate type matches pyroxene's oxygen-to-silicon ratio (the answer is cyclosilicates).

Polymorphs (both divisions) are different structures of the same chemical composition. The rules name four: diamond and graphite (carbon), calcite and aragonite (CaCO₃), orthoclase and microcline (KAlSi₃O₈), and the Al₂SiO₅ trio kyanite, andalusite and sillimanite. Each polymorph has different hardness, density or cleavage even though the formula is identical: diamond's three-dimensional covalent network makes it the hardest mineral, while graphite's sheets slide apart, making it soft and greasy.

Trace elements explain many color puzzles. Corundum is colorless when pure; trace chromium makes ruby red, and trace iron and titanium contribute to sapphire blue. The chemical formula tells you what the element list should be, and the color tells you which trace element to suspect.

Solid solutions, ternary diagrams and phase diagrams (Division C)

In a solid-solution series, one ion substitutes for another of similar size and charge, so the composition slides between two or more end members instead of jumping. Properties such as density, color and refractive index shift along with the composition. The 2027 Division C rules limit solid solutions to five groups:

The carbonate substitution is not equally complete between every pair: iron and manganese mix freely (siderite–rhodochrosite), while calcium mixes with them only partly, because Ca²⁺ is noticeably larger. If a question asks why a substitution is limited, ionic size is the answer to reach for.

Plagioclase is named by its percent anorthite (An):

A feldspar ternary diagram is a triangle with the three end members at the corners: potassium feldspar (orthoclase, Or), albite (Ab) and anorthite (An). A point's position says how much of each end member it contains, and the closer to a corner, the more of that end member. The plagioclase series lies along the Ab–An edge and the alkali feldspars along the Or–Ab edge. At lower temperatures the sodium-rich and potassium-rich feldspars do not mix completely, so an intermediate alkali feldspar can separate into two intergrown feldspars as it cools. That intergrowth is called perthite.

A phase diagram plots which phases (liquid, solid, or a mix) are stable at each temperature and composition (or temperature and pressure). The manual limits you to two-component systems. Read it in four steps:

1. Find the point for your composition and temperature.
2. If it sits above the liquidus, everything is liquid. If it sits below the solidus, everything is solid.
3. Between the two lines is a mixture. Draw a horizontal tie line through the point; where it meets the liquidus and solidus gives the compositions of the liquid and the solid.
4. At a eutectic (the lowest-melting composition of a system with no solid solution), the liquid freezes to a fine mixture of two minerals at one fixed temperature.

For a plagioclase-type loop the first crystals are richer in calcium than the melt, which is the diagram form of the continuous Bowen branch.

Crystal systems (Division C)

A crystal system groups minerals by the lengths and angles of their three crystallographic axes. It controls crystal shape and, because atoms are arranged differently along different directions, how the mineral cleaves.

Cubic symmetry makes cleavages repeat equally along symmetric directions: halite's weak planes give three cleavages at 90° (cubes), fluorite's give four (octahedra), and garnet's strong bonding in every direction gives no cleavage. Cubic minerals are also optically isotropic, which matters in thin section. Some sources treat trigonal minerals as a division of the hexagonal system, and at least one archived question groups quartz and corundum under "hexagonal", so check which scheme the supervisor or the question uses.

How minerals form

Minerals record the environment that made them, and the manual asks for methods of formation and for minerals typical of each rock-forming setting. The standard groupings are below; they are typical, not exhaustive.

Seawater evaporation precipitates salts in order of increasing solubility: carbonates first, then gypsum, then halite, then the potassium and magnesium salts, which stay dissolved longest.

What is a rock?

The 2027 rules define a rock as a naturally occurring solid mass of one or more minerals or of mineraloid matter. Three consequences follow, and each is a favorite true/false item:

• A rock can be monomineralic (one mineral, such as quartzite, marble, rock salt or rock gypsum) or polymineralic (several, such as granite with quartz, feldspar and mica).
• A rock can be made of mineraloid matter, such as volcanic glass (obsidian, pumice).
• Unlike a mineral, a rock can be made of organic matter: coal is compressed plant material. Biochemical rocks such as coquina and chalk are built from the shells of organisms.

To classify a rock into one of the three families, look for the diagnostic features the rules point to. Igneous rocks show interlocking crystals, glass or gas holes (vesicles). Sedimentary rocks show rounded grains, cement between grains, fossils or layers. Metamorphic rocks show foliation (aligned flat minerals) or banding, or interlocking recrystallized grains that clearly came from a known parent. When observation is not enough, the rules promise extra diagnostics, for example the mineral makeup of a fine-grained igneous rock or the acid reaction of chalk or diatomite (chalk fizzes, diatomite does not).

Igneous rocks

Igneous rocks form when molten rock (magma below ground, lava at the surface) cools and crystallizes. Two things control what you see: where the melt cooled (inside the crust or at the surface) and how fast it cooled. Slow cooling lets crystals grow large. Fast cooling leaves them small or leaves glass.

Texture: how it cooled

Phenocrysts tell a story. A crystal that grew large while the magma was still deep tells you there was a long slow stage before eruption, and the fine groundmass around it records the fast final cooling.

Composition: what it is made of

Composition is described on a scale from silica-rich to silica-poor. Silica content (SiO₂) also sets color: the more silica, the lighter the rock, because dark mafic minerals are rich in iron and magnesium.

The percentages are approximate class boundaries used in most textbooks. Color is a clue, not a test. A fine-grained dark rock can be basalt or a dark glassy rock, and a fine-grained light rock can be rhyolite. Confirm with texture and, where possible, the minerals visible in the sample.

The Bowen reaction series

Bowen's reaction series describes the order in which minerals crystallize from a cooling magma. It has two branches that meet at the bottom.

• Discontinuous branch (left): each mineral forms at a particular temperature and reacts with the melt to make the next. Olivine comes first, then pyroxene, amphibole and biotite. Each is a different mineral, so the change is discontinuous.
• Continuous branch (right): plagioclase feldspar forms across the whole range. Early crystals are calcium-rich and later ones are sodium-rich, so the composition changes gradually while the mineral stays plagioclase.
• The branches merge into potassium feldspar, then muscovite and quartz, which crystallize last at the lowest temperatures. The diagram's schematic temperature axis runs from about 1,300 °C at the top to about 540 °C at the bottom, and real crystallization temperatures shift with composition and water content.

If early crystals settle out and are removed, the remaining liquid becomes more silica-rich (fractional crystallization).

Where igneous rocks form

The 2027 rules limit igneous formations to three, one intrusive and two extrusive:

The texture tells you which setting you are in. A phaneritic specimen points to a batholith-type intrusion; a fine, vesicular or glassy one to a lava flow; a rock of welded ash and angular fragments to a pyroclastic deposit. Tuff is mostly ash-sized fragments (under 2 mm), while tuff breccia also contains larger angular blocks.

Plate tectonics links these rocks to where they form. Basalt forms at mid-ocean ridges, where decompression melting of the mantle produces mafic magma at divergent boundaries. Andesite and diorite are typical of subduction zones, where water released by the sinking plate lowers the melting point of the mantle above it and the resulting magma becomes intermediate as it rises through crust. Granite is typical of convergent continental margins and collision zones, where continental crust melts to give felsic magma.

Evolution of igneous melts (Division C)

A magma rarely keeps its original composition. The 2027 Division C rules name three ways it changes, and a test can ask you to recognize each from a description or a diagram.

Fractional crystallization follows directly from Bowen's series. Because the early minerals are poor in silica and rich in iron and magnesium, taking them out leaves a liquid that is relatively richer in silica. That is how one basaltic magma can, in stages, produce andesite and then rhyolite.

Incompatible elements are trace elements whose ions are the wrong size or charge to fit into the crystal sites of the common rock-forming minerals. Examples are lithium, beryllium, boron, rubidium, cesium, tantalum, niobium, the rare earth elements, uranium and thorium. As a magma crystallizes, the common minerals reject them, so their concentration in the shrinking liquid keeps rising. The last fraction of melt is therefore water-rich and loaded with these elements. That late fluid forms pegmatites: the water lets ions diffuse quickly, so crystals grow very large, and the concentrated incompatible elements finally become abundant enough to build their own minerals. This is why pegmatites host beryl (beryllium; emerald, aquamarine and morganite), spodumene (lithium; kunzite and hiddenite), lepidolite (lithium mica), tourmaline (boron) and many ore minerals of tantalum, cesium and the rare earths.

Sedimentary rocks

Sedimentary rocks form from pieces of other rocks (clastic), from minerals precipitated from water (chemical), or from the remains of organisms (biochemical). The 2027 rules limit sedimentary textures to exactly these three: clastic (also called detrital or terrigenous), chemical (crystalline) and biochemical (organic or bioclastic). Grain-size and environment questions are where most of the points are.

Grain size and sorting

Clastic grain size is the key classification tool, and it tells you the energy of the environment. Use the standard size scale (Wentworth):

Fine grains need low-energy water or air to settle (quiet lakes, the deep sea). Coarse grains need high energy (fast rivers, surf) to be moved at all. Rounding shows how far clasts traveled and how long they were tumbled: rounded grains have been worn in transport, and angular grains were not moved far. Sorting describes size uniformity. Well-sorted sediment came from a steady process; poorly sorted sediment was dumped quickly. Conglomerate is rounded and breccia is angular, which is a common question pair.

Grain size and stream velocity

The 2027 rules tie grain size directly to water velocity in rivers and streams. The standard tool is the Hjulström diagram (Hjulström curve), which plots grain size on the horizontal axis against flow velocity on the vertical axis, both on logarithmic scales. Two curves divide it into three fields.

• Erosion (upper curve). Above it, the flow can lift grains of that size off the bed. Fine to medium sand (about 0.1–0.5 mm) is the easiest sediment to erode, needing only roughly 20–30 cm/s. Coarser grains need more velocity because they are heavier.
• Clay and silt are hard to erode even though they are tiny. The flat platy particles stick together (cohesion) and form a smooth bed that the flow skims over, so the erosion curve rises again on the left of the diagram.
• Transportation (between the curves). A grain that is already moving keeps moving at velocities well below the one needed to pick it up.
• Deposition (below the lower curve). When the flow slows below the settling curve, grains of that size drop out. For clay the settling velocity is so low that clay stays suspended in almost any moving water and settles only in still water such as lakes, lagoons, floodplain ponds and the deep sea.

The same logic explains sorting and environments: high-velocity mountain streams and alluvial fans leave gravel, rivers in flood leave sand in their channels and silt on the floodplain, and only quiet water lets clay settle into what becomes shale.

Chemical and biochemical rocks

Coal is built mainly from organic carbon, and its rank increases with burial depth, heat and time. Anthracite is the highest rank and has the most carbon.

The clastic rocks on the National List are conglomerate and breccia (gravel), three kinds of sandstone (sand) and shale (mud). Siltstone and mudstone are useful comparison terms but are not on the list. The sandstone varieties are separated by what the sand is made of:

Mature versus immature is a common reasoning step: the more stable the grains (quartz) and the better sorted and rounded, the longer the transport.

Environments and primary structures

Each environment leaves a recognizable mix of grain size, sorting, rounding, composition and structures. The event expects you to link the two.

Primary structures are formed at deposition and tell you how the sediment moved. Plane bedding is layers with flat tops and bottoms. Cross-bedding is inclined layers inside beds, from migrating dunes and bars. Ripple marks are small symmetric or asymmetric ridges formed by water or wind flow. Mud cracks form when wet mud dries and shrinks, so the environment was exposed to air. Graded bedding is a bed that gets finer upward; it records a single deposition event such as a turbidity current. Fossil tracks and trails record living animals on the sediment surface.

Metamorphic rocks

Metamorphic rocks form when existing rock (the protolith) is changed by heat, pressure or hot fluids without melting it completely. Metamorphism recrystallizes minerals into new ones that are stable under the new conditions. The protolith usually controls the chemistry: a limestone protolith gives calcite-rich marble, and a sandstone protolith gives quartz-rich quartzite.

Texture: foliated or not

Foliation is a planar fabric from directed pressure: platy minerals (mica, chlorite) grow perpendicular to the squeeze, so the rock splits into sheets. Non-foliated rocks have crystals that grow in all directions, usually because the protolith was already equidimensional (limestone, quartz sand) or because the heat was contact heat without strong directed stress.

The slate–phyllite–schist–gneiss sequence is an increasing-grade sequence. Grain size rises with grade, and the banding becomes more pronounced: from invisible grains in slate to coarse segregated bands in gneiss. Slate comes in several colors because of its impurities: carbon-rich material makes it dark or black, iron oxide makes it red, and chlorite makes it green.

The rules give five protolith pairs to know cold: shale → slate, limestone → marble, sandstone → quartzite, peridotite → serpentinite, and basalt or gabbro → amphibolite. The last two are about mantle and oceanic rock: water added to olivine-rich peridotite turns it into green serpentine minerals, and basalt or gabbro heated and squeezed under wet conditions turns its pyroxene into hornblende.

The marble and quartzite rows show why the protolith matters. Marble and quartzite are non-foliated because their parent minerals (calcite, quartz) are equidimensional and have no platy minerals to align; they are also the metamorphic rocks most easily confused with their sedimentary parents. Quartzite breaks through the grains because the quartz has fused, whereas sandstone breaks around them.

Grade and index minerals

Grade is the intensity of metamorphism (low, medium, high). An index mineral forms only within a particular range of temperature and pressure, so finding one tells you the conditions the rock reached. The 2027 rules close the index-mineral list at seven. Six of them (chlorite, biotite, garnet, staurolite, kyanite, sillimanite) are the classic Barrovian zones mapped in metamorphosed shale; muscovite is added as a low-grade mica that coarsens before biotite appears. In order of increasing grade:

The line on a map where an index mineral first appears is an isograd, a line of equal grade. Crossing isograds toward a mountain core means rising temperature and pressure. Muscovite is the one to read carefully: fine white mica already grows in slate, so as a grade marker it means coarse flakes you can see, and at the highest grades muscovite breaks down, releasing the aluminum and potassium that help sillimanite and potassium feldspar form in gneiss.

Other metamorphic minerals the rules name, but not as index minerals, are corundum, epidote and andalusite. Epidote is common in greenschist-facies rocks, so it still indicates low-grade metamorphism of mafic rock, but it is not on the 2027 index list. Kyanite, andalusite and sillimanite are polymorphs of Al₂SiO₅, so they tell you about pressure as well as temperature: andalusite forms at low pressure, kyanite at high pressure, and sillimanite at high temperature. A rock containing kyanite therefore came from deeper, more compressed conditions than one with andalusite, even though the chemistry is the same.

Regional and contact metamorphism

Regional metamorphism happens over large areas, usually during mountain building, when rock is buried and squeezed. It produces foliated rocks with a range of grades. Contact metamorphism happens next to an intrusion, where heat from the magma bakes the surrounding rock with little directed pressure. It produces non-foliated rocks such as hornfels in a narrow zone around the intrusion.

Metamorphic facies (Division C)

A metamorphic facies is a set of mineral assemblages that form together under a given range of pressure and temperature. Facies are read from a pressure–temperature (or depth–temperature) graph, so know where each sits relative to the others:

Pressure rises with depth, so the vertical axis is also a depth axis. The key contrast is the temperature gained per kilometer of depth: a steep geotherm (near an intrusion) makes hornfels, a moderate one (continental collision) makes the greenschist–amphibolite–granulite path, and a very low one (subducting slab) makes blueschist and eclogite.

Plate-tectonic settings (Division C). Regional metamorphism and mountain building occur where continents collide. Blueschist and eclogite form in subduction zones. Greenstone and greenschist form from basalt or gabbro at ocean-crust divergent boundaries, where hot water circulates through new crust.

Thin sections (Division C, State and National)

Advanced tournaments show photomicrographs: photographs of a rock slice ground thin enough for light to pass through, taken through a polarizing microscope. Under crossed polarizers minerals show interference colors that depend on their optical properties. The rules limit mineral identification to five minerals and name four optical features to use:

• Twinning: plagioclase shows fine parallel stripes (polysynthetic twinning), while microcline shows a crosshatched "tartan" pattern.
• Extinction: as the stage rotates, a crystal goes dark at set angles. Garnet is isotropic (cubic), so it stays dark at every angle.
• Cleavage planes: thin dark lines in the crystal. Calcite shows rhombohedral cleavage; augite shows two cleavages near 90° that cut an eight-sided cross section.
• Birefringence: the strength of the interference colors. Calcite shows very high, pale pastel colors.

The manual also asks you to tell rock types apart by microscopic texture: holocrystalline (fully crystalline) igneous rock versus vesicular or glassy rock (basalt versus pumice); porphyritic igneous texture; and sedimentary rocks distinguished by rounded or angular grains, good or poor sorting and skeletal fragments, for example oolites or sandstone versus arkose. Use the same logic as with hand specimens: crystal size, bubbles, grain shape and sorting.

The rock cycle and uses of rocks and minerals

The rock cycle links the three rock families. Igneous rock can be weathered and eroded into sediment, which is buried, compacted and cemented into sedimentary rock. Buried rock can be heated and squeezed into metamorphic rock, and very hot rock can melt to make magma that cools into igneous rock again. Every step is a process, so the event tests the processes more than the labels.

Uses of rocks and minerals

The rules ask for the economic uses of minerals and rocks, and the listed examples give a good map: ores, industry, jewelry, geochronology, medicine, manufacturing, construction and electronics.

• Ores. Chalcopyrite and bornite for copper; hematite and magnetite for iron; galena for lead; sphalerite for zinc; bauxite (a sedimentary rock on the National List) for aluminum.
• Construction and ornamental. Granite, marble, limestone and slate as building and dimension stone; gypsum for plaster and wallboard; sand and gravel for concrete; limestone for cement.
• Agriculture. Crushed limestone neutralizes acidic soil, gypsum conditions soil, and phosphate minerals such as apatite supply phosphorus for fertilizer.
• Fossil fuels. Coal is a sedimentary rock and an energy source, and porous sandstone and limestone can hold oil and gas.
• Electronics and industry. Quartz is piezoelectric (it generates a voltage when squeezed) and is used in oscillators and sensors; graphite lubricates and conducts; halite is a source of sodium and chlorine.
• Gemstones. Precious and semi-precious minerals on the National List count (for example topaz, tourmaline, garnet, amethyst, citrine, turquoise, zircon), plus a closed list of named varieties in the 2027 rules. Know each variety's parent mineral and what colors it:

• Geochronology. Radioactive isotopes decay at a fixed rate, so the ratio of parent to daughter isotope dates a rock. The method works because the decay is controlled by a half-life, not by temperature or pressure. Zircon is the standard mineral for uranium–lead dating because it takes uranium into its structure when it crystallizes but excludes lead.

Strategy

• Split by skill, but rotate. At a station event, both partners move together. For paper sections, one partner takes identification and the other takes classification and data. Swap halfway so both of you can check the other's reasoning.
• Build a one-page identification flow. Start with luster (metallic or not), then streak, hardness, cleavage, reaction to acid, and density. For rocks, start with crystal size and whether there are crystals, then glass or vesicles, then clasts, then foliation. Write the flow at the top of your binder, and mark each test as you complete it.
• Binder priorities. The Mohs anchors; the streak and cleavage table; the silicate table; the composition and texture tables; the Bowen diagram; the sedimentary grain-size table and environment table; the metamorphic protolith and index-mineral table; the half-life formula with one example; and the rock cycle diagram. Add one line per footnote-1 specimen (magnesite, bornite, willemite, syenite, tuff, tuff breccia, diatomite) listing the information a supervisor is likely to give. Leave out anything that is not on the list of rules topics or the National List.
• Explain in one or two sentences. A strong answer names the process and the evidence: "The rock is vesicular and fine-grained, so it cooled rapidly at the surface with gas trapped in the melt." Partial credit follows reasoning.
• Budget time. Station times are fixed and cannot be extended. If a specimen stumps you, write the best observation-based answer, then move on. Identification is capped at half the points, so you do not need every name to score well.
• Practice on the list. Work through the National List once, naming each mineral's streak, hardness and cleavage and each rock's texture and origin from memory. Then practice with archived tests from several different writers.

Common pitfalls

How tournaments test this

The archive has 9,189 Rocks and Minerals questions from public tests, including 5,212 Division C questions, 3,410 Division B questions and 567 tagged for both divisions. The practice bank adds 7,229 questions. Most of the archive is from the 2022 season (1,809) and the 2026 season (5,084), which means the event's current style is well represented.

• Format. About 80% of archived questions are free response (7,400), 14% are multiple choice (1,332), 3% are true/false (248) and 2% are select-all (180). Expect to write sentences, so practice explaining a result in one or two lines.
• Topics (tags overlap). Mineral properties appear on 5,290 questions, igneous on 1,622, sedimentary on 1,327, rock types on 1,268, metamorphic on 1,046 and crystal systems on 549.
• Task shapes. The largest labeled task is "explain or why" (6.7% of the archive), followed by "which of the following" (2.3%), compare and contrast (1.3%), true/false (1.1%), identify or name a structure in a figure (0.8%), definition (0.7%), calculate (0.5%) and interpret a graph, table or curve (0.5%). Most questions do not carry a task label, so these shares show the common shapes rather than a full breakdown.
• Recurring terms. "Mineral" appears in about 3,400 questions, "rock" in 2,600, "specimen" in 2,600, "igneous" in 757, "metamorphic" in 689, "sedimentary" in 673, "crystal" in 647, "hardness" in 547, "Mohs" in 224, "chemical formula" in 301, "reaction series" in 289, "Bowen reaction" in 230, "specific gravity" in 192, "hydrochloric acid" in 82 and "index mineral" in 48.
• Most common correct answers. Olivine (51 questions), calcite (50), limestone (43), quartz (43), igneous (42), sedimentary (38), basalt (37), granite (33), gneiss (30), pyrite (27), halite (26) and marble (25). Know these, including what distinguishes each from the others it is commonly confused with.
• Typical shapes. A specimen described by properties with the question "which mineral is it?"; a set of tests with the question "which result rules out X?"; a Hjulström-diagram reading of which grain size moves at a given velocity; a Bowen's series question about which mineral forms first or what changes with temperature; a sedimentary environment asked from grain size and structure; a metamorphic question asking for a protolith, an index mineral or a grade; and a rock-cycle process asked in words.

Test yourself

Real questions from public tournament tests in the Scio.ly archive. Click an answer to check it; each links to the full test. Explanations are added where the reasoning is not obvious from the answer alone.

Test yourselfMinerals: identity, tests and chemistry

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   Which mineral is a polymorph of graphite?

   Question 1 options

   AHaliteBOlivineCMicroclineDDiamond

   From: Raisbeck Aviation Invitational - WA, 2025-26, Division C

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Test yourselfIgneous rocks, Bowen's series and melt evolution

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1. 1

   What does it mean for a rock to be plutonic?

   Question 1 options

   AA rock that comes from PlutoBA rock that cools on the inside of the earthCA rock that cools exposed to the atmosphereDAny igneous rockEA rock from rapid cooling after being thrown into water or similar cool liquid

   From: CSE (Captains Summer Exchange), 2025-26, Division C

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Test yourselfSedimentary, metamorphic and the rock cycle

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1. 1

   What type of rock is most likely to contain fossils?

   Question 1 options

   AIgneousBSedimentaryCMetamorphicDAll are equally likely

   From: CrabSO Invitational - MD, 2025-26, Division B

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References and further reading

• Steven Earle, Physical Geology (open textbook), chapters on minerals, igneous, sedimentary and metamorphic rocks, and weathering: https://opentextbc.ca/physicalgeology2ed/
• Mindat, mineral database with photos, chemistry and physical properties: https://www.mindat.org
• USGS, earth science and geologic topics, including mineral and rock resources: https://www.usgs.gov
• Wikipedia, Mohs scale of mineral hardness (for the hardness anchors): https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness
• Wikipedia, Bowen's reaction series (for a second diagram of the series): https://en.wikipedia.org/wiki/Bowen%27s_reaction_series
• Science Olympiad Rocks and Minerals event page (rules, National List and official resources): https://www.soinc.org
• SciOly Wiki, Rocks and Minerals (another summary of the event): https://scioly.org/wiki/index.php/Rocks_and_Minerals
• Practice more: the Scio.ly test archive has hundreds of public Rocks and Minerals tests, and the Dynamic Planet guide covers the Earth-science background behind many of the same processes.