Minerals

A mineral is a naturally occurring solid with a specific chemical composition and a regular crystal structure. Rocks are made of one or more minerals fitted together. Over 5,000 different minerals have been identified, although only a few dozen are common enough to be everyday rocks. Minerals are not just the building blocks of the Earth: they are also the raw materials for almost everything we make, from buildings and phones to rocket engines and toothpaste. Identifying them is one of the most useful skills in earth science.

• Total known mineralsOver 5,000Plus new ones found each year
• Most common mineralFeldsparApproximately 60% of Earth's crust
• HardestDiamondMohs scale 10
• SoftestTalcMohs scale 1, soft enough to scratch with a fingernail
• Most usefulQuartzGlass, electronics, watches, lasers
• Most precious metalRhodiumEven rarer than gold

What makes something a mineral?

Strictly speaking, to count as a mineral something has to be:

• Naturally occurring: not made by humans in a factory.
• Solid: not liquid or gas.
• Inorganic: not made by living things (so coal, although natural and solid, is technically not a mineral).
• Has a specific chemical composition: written as a chemical formula.
• Has a regular crystal structure: the atoms are arranged in a repeating pattern.

The most common minerals

Most rocks are made from a small handful of common minerals.

• Feldspar: the most abundant mineral group in Earth's crust. Found in most igneous and metamorphic rocks.
• Quartz: silicon dioxide. One of the hardest common minerals. Found in granite, sandstone and almost every beach.
• Mica: forms thin flexible sheets. Found in many rocks, often as shiny silvery flakes.
• Calcite: calcium carbonate. The main mineral in limestone and marble.
• Pyroxene and amphibole: dark minerals common in igneous and metamorphic rocks.
• Olivine: a green mineral found in deep Earth rocks and meteorites.

The Mohs hardness scale

One of the most useful properties of a mineral is its hardness: how hard it is to scratch. In 1812, German mineralogist Friedrich Mohs set up a scale based on 10 reference minerals, from softest (1) to hardest (10).

1. Talc: softer than a fingernail.
2. Gypsum: can be scratched with a fingernail.
3. Calcite: scratched with a copper coin.
4. Fluorite: scratched with a steel knife.
5. Apatite: scratched with a steel knife (but harder).
6. Orthoclase: scratched with a steel file.
7. Quartz: scratches glass.
8. Topaz: scratches quartz.
9. Corundum (sapphire and ruby): scratches topaz.
10. Diamond: the hardest natural substance. Only another diamond can scratch it.

The scale is not perfectly even: diamond is approximately 4 times harder than corundum, but only one step up on the Mohs scale. The scale is useful in the field because you can quickly identify what something is by trying to scratch it with everyday tools.

How to identify a mineral

• Colour: helpful but not definitive (many minerals come in several colours).
• Streak: the colour of the powder when scraped on a porcelain plate. Often more reliable than the overall colour.
• Lustre: how shiny it is. Glassy, metallic, pearly, silky, dull?
• Hardness: tested using the Mohs scale.
• Cleavage: how the mineral breaks. Some minerals split into smooth flat surfaces.
• Crystal shape: cubic, hexagonal, prismatic and many others.
• Density: heavier or lighter than expected for its size?
• Special properties: magnetism (magnetite), fluorescence under UV (fluorite), reaction with acid (calcite fizzes).

Fact Diamonds and the soft black graphite in pencils are both made of pure carbon. The difference is just how the atoms are arranged. In diamond, each carbon atom is bonded to four others in a rigid 3D lattice, making it the hardest natural substance. In graphite, atoms are arranged in flat layers that slide easily over each other, making it soft enough to leave a mark on paper. Two completely different minerals, same atoms.

Why minerals matter

• Construction: gypsum for plaster, calcite for cement, halite (rock salt) for water softening, quartz for glass.
• Metals: bauxite for aluminium, hematite for iron, chalcopyrite for copper, sphalerite for zinc, cassiterite for tin.
• Electronics: silicon (from quartz) for chips, lithium for batteries, copper and gold for wiring, neodymium for magnets.
• Energy: uranium ore for nuclear, lithium for electric car batteries.
• Jewellery: diamond, ruby, sapphire, emerald, opal, jade.
• Medicines: trace minerals like iron, magnesium, zinc and calcium are essential for health.
• Even toothpaste: contains powdered minerals (calcite, silica, fluoride) to scrub and protect teeth.

Did you know? The natural world contains over 5,000 known minerals, but most of the world is made from just a few dozen. Scientists keep finding more, often in unusual environments like deep mines, the ocean floor and tiny inclusions in older rocks. Some new minerals are extremely rare: only a single small specimen has ever been found.

Deeper dive: why your phone contains 30 different minerals

The smartphone you use every day contains an astonishing number of different minerals, mostly in tiny amounts but absolutely essential for the phone to work. A typical modern smartphone uses approximately 30 different elements, each derived from one or more minerals.

Some examples:

• Lithium (from minerals like spodumene): in the battery.
• Cobalt (from cobaltite and other ores): also in the battery.
• Silicon (from quartz): the basic chip material.
• Gold, silver and copper: in the wires and connectors.
• Aluminium (from bauxite): the case.
• Iron (from hematite): in steel parts.
• Neodymium, praseodymium and dysprosium: rare earth elements used in the tiny magnets in speakers and vibration motors.
• Indium: used in transparent conductive coatings for touchscreens.
• Tantalum (from coltan ore): in tiny capacitors.
• Tin (from cassiterite): in solder joins.

Many of these minerals are mined in just a few specific places in the world, often in regions with serious humanitarian or environmental issues. Coltan mining in central Africa, for example, has been linked to civil wars and human rights abuses. This is one reason recycling old electronics matters so much: a single mobile phone contains many times more gold per gram than typical gold ore. Future "urban mining" of old electronics may eventually be a significant source of rare metals for new ones.

For more, see crystals, famous gems and what is a rock.