In a real lab, wear safety glasses, use only very dilute acid (or vinegar for calcite) and never taste samples. Hardness values are on the Mohs scale; specific gravity (SG) is how many times as heavy as the same volume of water. For the copper coin test use pure copper, such as a US penny made before 1982: newer US pennies are mostly zinc and euro cent coins are copper-plated steel.
In 1812 Friedrich Mohs ranked ten minerals by which one scratches which. A harder mineral always scratches a softer one. Pick any two minerals or tools and rub them together.
The Mohs scale only gives the order, not how much harder: corundum (9) is about twice as hard as topaz (8), but diamond (10) is about four times as hard as corundum.
Five unknown minerals from the Mohs scale are labeled A to E. Scratch pairs of them to find out which is harder, then arrange them from softest (top) to hardest (bottom) and press Check.
Rocks are mixtures of minerals, so geologists name them by their texture (grains, crystals, layers, holes) and a few tests. Read the field notes, then answer the yes/no questions of the key until it names the rock. Twelve common rocks; for how each one forms, see the rock cycle page.
Geologists identify minerals with a few simple tools. Pick Basic (8 labels) or Advanced (12). Switch between the labeled diagram, a blank one, a label quiz and match the jobs. On a phone, swipe the diagram sideways.
Tap a word, then tap the numbered box it belongs to (on the diagram or in the list below). Tap a filled box to take the word back.
Each line describes the job of one part. Tap a part name, then tap the box next to the job it does. Tap a filled box to take the word back.
Tap a card, then tap the box it belongs in. Press Check when all 12 are placed.
A printable worksheet: label the testing kit, sort 12 items into mineral, rock or neither, fill in the blanks, multiple choice, and identify four mystery minerals from their test results, with an answer key. The label part uses the level chosen in the diagram above.
A mineral is a natural, non-living solid with a definite chemical makeup and its atoms arranged in a regular pattern (a crystal structure). Quartz, salt (halite) and gold are minerals. A rock is a natural mixture of one or more minerals: granite is quartz + feldspar + mica. Glass, steel and sugar are not minerals: they are made by people or by living things, or have no crystal structure.
Color is easy to see but often misleading. Luster is how the surface reflects light: metallic or non-metallic (glassy, pearly, silky, dull). Streak is the color of the powder on a streak plate and is much more reliable. Hardness is tested by scratching (Mohs scale). Cleavage means splitting along flat surfaces; fracture means breaking unevenly or in curves. Special tests help too: magnetism (magnetite), fizzing in acid (calcite), density (galena, gold), taste and glow (never taste in a lab).
The properties come from the atoms and how strongly they are bonded. Cleavage happens along planes of weak bonds: mica’s sheets are held together only weakly, halite’s cubic crystal splits along three planes at 90°. Quartz has strong bonds in all directions, so it has no cleavage and is hard. Calcite fizzes because acid reacts with its carbonate: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Density depends on how heavy the atoms are and how tightly they pack: galena contains lead, gold is pure heavy metal.
Almost everything around us comes from minerals: glass from quartz sand, plaster from gypsum, iron and steel from hematite and magnetite, aluminum from bauxite ore, copper wires, phone batteries and pencil “lead” (graphite). Mineral resources are found in only some places and take millions of years to form, so recycling and careful mining matter.
Compare pyrite and gold with the streak plate and the scratch test. Rub hematite on the streak plate. Break halite, calcite and mica to see three kinds of cleavage. Then switch to Mystery sample and try to identify it with as few tests as possible.
| Mineral | Color | Luster | Streak | Hardness (Mohs) | Cleavage / fracture | Specific gravity | Best clue |
|---|---|---|---|---|---|---|---|
| Quartz | Colorless, white, many colors | Glassy | None (harder than plate) | 7 | None; conchoidal fracture | 2.65 | Scratches glass; six-sided crystals |
| Feldspar (orthoclase) | Pink, white, gray | Glassy to pearly | White | 6 | 2 at about 90° (blocky) | 2.56 | Most common minerals in the crust |
| Mica (muscovite) | Colorless, silvery | Pearly | White | 2–2.5 | 1 perfect: thin elastic sheets | 2.8 | Sheets bend and spring back |
| Calcite | Colorless, white | Glassy | White | 3 | 3 not at 90° (rhombs) | 2.71 | Fizzes in dilute acid; double image |
| Halite | Colorless, white | Glassy | White | 2.5 | 3 at 90° (cubes) | 2.17 | Salty; dissolves in water |
| Gypsum | White, colorless | Glassy to silky | White | 2 | 1 perfect (plates) | 2.3 | Fingernail scratches it |
| Talc | White, pale green | Pearly to greasy | White | 1 | 1 (flakes) | 2.75 | Feels soapy |
| Fluorite | Purple, green, yellow | Glassy | White | 4 | 4 (octahedrons) | 3.18 | Often glows under UV light |
| Pyrite | Brassy yellow | Metallic | Greenish-black | 6–6.5 | None; uneven fracture | 5.0 | “Fool’s gold”; striped cubes |
| Gold | Gold yellow | Metallic | Golden yellow | 2.5–3 | None; bends (malleable) | 19.3 | Extremely heavy; never tarnishes |
| Galena | Lead gray | Metallic | Lead gray | 2.5 | 3 at 90° (cubes) | 7.5 | Very heavy; lead ore |
| Magnetite | Black | Metallic | Black | 5.5–6.5 | None; uneven fracture | 5.2 | Strongly magnetic |
| Hematite | Silvery gray, black, red | Metallic to dull | Red-brown | 5–6.5 | None; uneven fracture | 5.3 | Red-brown streak; iron ore |
| Graphite | Black, steel gray | Metallic to dull | Black to gray-black | 1–2 | 1 perfect (flakes) | 2.2 | Greasy; marks paper |
| Hardness | Mineral | Everyday test |
|---|---|---|
| 1 | Talc | Scratched by a fingernail (about 2.5) |
| 2 | Gypsum | |
| 3 | Calcite | Scratched by pure copper, such as an old copper coin (about 3.5) |
| 4 | Fluorite | Scratched by a steel nail or knife (about 5.5) |
| 5 | Apatite | |
| 6 | Orthoclase feldspar | Scratches glass (5.5); 7 scratches a steel file |
| 7 | Quartz | |
| 8 | Topaz | Scratches quartz; used as gems and abrasives |
| 9 | Corundum (ruby, sapphire) | |
| 10 | Diamond |
Quartz (gray, glassy), feldspar (pink or white) and mica or hornblende (black): crystals big enough to see because the magma cooled slowly.
Made mostly of the mineral calcite, so both fizz in acid. Limestone often contains shell fossils; marble is limestone changed by heat and pressure.
Sand grains, mostly quartz, cemented together. Because quartz is hard and does not weather easily, it survives as sand on beaches and in deserts.
A mineral is a single natural, non-living solid with a definite chemical makeup and an ordered crystal structure, such as quartz or calcite. A rock is a natural mixture of one or more minerals (and sometimes glass or fossils). Granite, for example, is a rock made of the minerals quartz, feldspar and mica.
Key takeaway: minerals are the ingredients, rocks are the mixtures.Color, luster (how it shines), streak (the color of its powder), hardness (scratch test on the Mohs scale), cleavage or fracture (how it breaks), density or specific gravity (how heavy it feels), crystal shape, and special properties such as magnetism, fizzing in acid, fluorescence, taste or smell.
Key takeaway: luster, streak, hardness and cleavage are the most useful.Rub a corner of the mineral firmly across an unglazed white porcelain tile (a streak plate) and look at the color of the powder line. The streak color stays the same even when the mineral comes in different colors. Minerals harder than the plate (about 6.5), such as quartz, leave no streak and scratch the plate instead.
Key takeaway: the streak is the color of the powder.A scale from 1 to 10 made by Friedrich Mohs in 1812, using ten reference minerals: talc 1, gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase feldspar 6, quartz 7, topaz 8, corundum 9 and diamond 10. Each mineral scratches the ones below it. It shows order only: diamond is about four times as hard as corundum.
Key takeaway: a harder mineral scratches a softer one.Cleavage is when a mineral splits along smooth, flat surfaces, because some directions in its crystal have weaker bonds: halite breaks into cubes, mica peels into sheets. Fracture is when it breaks along rough, uneven or curved surfaces, because the bonds are about equally strong in all directions: quartz has curved, shell-like (conchoidal) fracture.
Key takeaway: cleavage is flat and smooth; fracture is rough or curved.Pyrite gives a greenish-black streak, is hard enough to scratch glass (6 to 6.5) and breaks when hit. Gold gives a golden-yellow streak, is soft (2.5 to 3), bends and flattens instead of breaking, and is about four times as heavy as pyrite.
Key takeaway: streak, hardness and weight give fool’s gold away.Tiny amounts of other elements can change a mineral’s color: quartz can be clear, white, purple (amethyst), pink, yellow or smoky brown. Weathered surfaces can also look different from fresh ones. Streak, hardness and cleavage stay the same, so they are better clues.
Key takeaway: the same mineral can come in many colors.Geologists measure specific gravity: how many times as heavy a mineral is as the same volume of water. Weigh the sample in air, then in water; the difference is the weight of the water it pushes aside. Simply holding similar-sized samples (hefting) already shows that galena or gold feel much heavier than quartz.
Key takeaway: heavy metal minerals have a high specific gravity.Almost everything: quartz sand for glass and computer chips, gypsum for plaster and drywall, halite for salt, hematite and magnetite for iron and steel, galena for lead, graphite for pencils and batteries, talc for powders, fluorite for steel-making, feldspar for ceramics, and gold for electronics and jewelry.
Key takeaway: our buildings, tools and electronics come from minerals.The test results follow real mineral data (Mohs hardness, streak, luster, cleavage, specific gravity, magnetism and the acid test), but the 3D specimens are simplified models, colors vary in nature, and the tools are idealized: real hardness tests can be borderline, so geologists combine several tests. Safety in a real lab: goggles, very dilute acid, never taste samples.
Key takeaway: real data, simplified specimens.