Minerals

In every survival game, the first thing you do is start mining. Stone, coal, iron, and if you're lucky, diamonds. Guess what? Real Earth works the same way. Those things are all minerals (well, coal is a rock, but we'll get to that).

Not everything you dig up is a mineral. To make the list, it has to pass five tests:

1. Naturally occurring. Made by nature, not in a factory.
2. Inorganic. Not made by living things. (Sorry, seashells and pearls are close calls.)
3. Solid. No liquids or gases allowed.
4. Definite chemical makeup. Same recipe every time. Quartz is always silicon and oxygen.
5. Crystal structure. Its atoms line up in a repeating pattern, like perfectly stacked blocks.

There are over 5,000 known minerals. But only about 20 or so are common, and those make up most of the rocks on Earth.

• Silicates: contain silicon and oxygen. These make up over 90% of Earth's crust. Quartz and feldspar are the superstars.
• Carbonates: contain carbon and oxygen. Calcite is one, and it fizzes when you drop acid on it.
• Oxides: metals bonded to oxygen. Hematite is an iron ore, and it's where a lot of our iron comes from.
• Native elements: pure elements found on their own. Gold, silver, copper, and diamond (pure carbon).

Geologists ID minerals like detectives, using clues called properties:

• Color: the easiest clue, but also the sneakiest. One mineral can come in many colors.
• Streak: the color of its powder when you scrape it on a white tile. Hematite can look silver or black, but its streak is always reddish-brown. Busted.
• Luster: how it shines. Metallic (like a shiny coin) or nonmetallic (glassy, pearly, dull, greasy).
• Hardness: how easily it scratches.
• Cleavage and fracture: how it breaks. Cleavage means it splits along flat, smooth surfaces. Fracture means it breaks rough or curvy, like broken glass.
• Density: how heavy it feels for its size. Gold is crazy heavy.
• Special properties: magnetite sticks to magnets, calcite fizzes in acid, and halite (rock salt) tastes salty. Don't lick rocks in class, though.

In 1812, a German scientist named Friedrich Mohs ranked 10 minerals from softest to hardest. Each one scratches the ones below it.

1. Talc (so soft your fingernail scratches it)
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Feldspar
7. Quartz
8. Topaz
9. Corundum (rubies and sapphires)
10. Diamond (the boss level)

Handy tools for testing: your fingernail is about 2.5, a copper penny about 3.5, a steel nail or glass about 5.5.

• A gem is a mineral that's rare, hard, and beautiful enough to be cut and polished. Diamonds, rubies, emeralds.
• An ore is a mineral we can mine for a profit, usually for a metal. Iron from hematite, aluminum from bauxite, copper from chalcopyrite.

Idaho is nicknamed the Gem State for a reason. It has over 70 kinds of gems, and it's one of the only places on Earth where you'll find star garnets.

You use minerals all day. Your phone has over 30 different elements from minerals in it. Toothpaste has fluorite. Pencil "lead" is actually graphite. Drywall is gypsum. Even the salt on your food is the mineral halite.