Look closely at granite and you see white, pink, black and glittering grains mixed together; each grain is a mineral, and a rock is what you get when minerals come together.
A mineral is a solid formed in nature whose atoms are arranged in a regular crystal, so each kind has its own shape and properties, like the six-sided columns of quartz or the thin sheets of mica.
That is why checking properties one by one, such as color, hardness, streak, reaction with acid and magnetism, lets you tell minerals apart, and hardness is compared against the Mohs scale, from talc at 1 to diamond at 10.
Pick the six minerals one at a time and compare their crystal shapes, hardness and uses, and you will see why quartz becomes glass and diamond is used for cutting.
Minerals and Rocks
💎 Minerals and Rocks
①A mineral is a solid formed in nature, with a fixed composition and atoms arranged regularly in a crystal.
②A rock is made of several minerals together; granite is a mix of quartz, feldspar and biotite.
③Feldspar is the most common mineral in the crust, followed by quartz.
④Different crystal structures give different properties even to minerals of the same element: diamond and graphite are both carbon but differ hugely in hardness.
Properties That Identify Minerals
Quartz
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The crystal shape, Mohs hardness and uses of the chosen mineral
Mohs hardness scale
Comparing hardness (a relative order found by scratching)
Hardness
Mineral
How to check
1
Talc
Scratched by a fingernail
3
Calcite
Scratched by a copper coin
5
Apatite
Scratched by a knife
7
Quartz
Scratches glass
10
Diamond
Hardest, scratches everything
Using Mineral Resources
Mineral resources
Resources sorted by use
⚠️ Properties That Identify Minerals
①Color: the first thing you notice, but impurities can change it, so it is a weak clue.
②Streak: the color of the powder left when the mineral is rubbed on an unglazed white tile; it is more reliable than color. Pyrite and chalcopyrite are both yellow, but their streaks are black and greenish black.
③Hardness: rub two minerals together; the one that gets scratched is softer.
④Reaction with acid: a drop of dilute hydrochloric acid on calcite fizzes (carbon dioxide).
⑤Magnetism: magnetite attracts iron objects such as paper clips.
Summary
Mineral
mineral = a naturally formed solid crystal of fixed composition
Identified by color, streak, hardness, reaction with acid and magnetism.
Mohs hardness scale
1 (talc) ~ 10 (diamond)
A relative order of ten reference minerals found by scratching them against each other; the numbers do not mean one is that many times harder.
🎯 Exam Points
①Minerals are identified by color, streak, hardness, reaction with acid, magnetism and so on.
②Mohs scale: talc (1) to diamond (10); a harder mineral scratches a softer one.
③Streak is the color of the powder on a streak plate, a more reliable clue than surface color.
④A rock is a group of minerals.
⑤Mineral resources take an extremely long time to form and are limited, so they must be used carefully and recycled.
Examples and Unit Test
Example 1
How do minerals differ from rocks, and what properties identify minerals?
1
A mineral is a naturally formed solid of fixed composition; a rock is made of several minerals together.
2
Minerals are identified by their own properties, such as color, streak, hardness, reaction with acid and magnetism.
▸ Mineral = solid of fixed composition / rock = group of minerals; identified by color, streak, hardness and so on
Judging by color alone often goes wrong, so check streak and hardness as well.
Example 2
On the Mohs scale, which is harder, quartz (7) or talc (1)? What happens if quartz is rubbed against talc?
1
On the Mohs scale, the larger the number, the harder the mineral (talc 1 to diamond 10).
2
Quartz (7) is harder than talc (1), so rubbing quartz on talc leaves a scratch on the talc.
▸ Quartz is harder / the talc gets scratched
In a scratch test the mark is always left on the softer one; compare the bars for quartz and talc in the picture and the gap is plain.
Unit-test style
Which statement about minerals and mineral resources is correct?
①A rock is made of only one kind of mineral
②On the Mohs scale, a higher number means a harder mineral
③Diamond is softer than talc
④Mineral resources are unlimited, so there is no need to save them
⑤Iron ore is a non-metallic mineral
▸ ② On the Mohs scale, a higher number means a harder mineral
1
On the Mohs scale, the larger the number, the harder the mineral, so ② is correct.
2
A rock is made of several minerals (①), diamond (10) is harder than talc (1) (③), mineral resources are limited and must be used carefully (④), and iron ore is a metallic mineral (⑤).