What "Large Deposits" Means

This part of the definition is not as definite as the other parts. How large is "large?" Generally it means that the deposit is large enough to show up on a geologic map.

To explore this, we will use the same materials that we used to explore "naturally occurring." You will need as many of the items from the following list as you can find:

  • several mineral specimens
  • several rock specimens
  • coins, bone, teeth, sea shells, wood, nails, cloth, glass, feather, paper, water, salt, pepper, other objects made of different materials

So which of these things form large layers or deposits in the Earth? Look at the piece of shale with the fossil fish that is beside the bottle of water. This is from the Green River Shale, a layer of rock that is over 1000 feet thick and covers many square miles, extending into Utah, Wyoming, and Colorado. That definitely counts as a large deposit.

Below that is the dish of dirt from an area where it covers many square miles. Again, that is a large deposit.

The lightbulb salt shaker contains salt. Does salt form large deposits? Just west of Salt Lake City in Utah is the Bonneville Salt Flats, a huge deposit of salt.

The black specimen to the right of the salt shaker is a piece of obsidian from a lava flow near Lee Vining, California. That lava flow covers many miles, again making it a large deposit.

Below the obsidian is a tan and dark gray pebble that is made of granite. Although this pebble is small, if you traced it back to its origin, you would find a huge area of granite over 20 miles across.

It may seem that any mineral would form large deposits, but many of them do not. Think about gemstones such as garnets, rubies, emeralds, and diamonds. Is there anyplace where you find a deposit of solid diamond that is several miles across? No. You can find large deposits of volcanic rock called kimberlite which can contain diamonds. The kimberlite is considered a rock, but the diamonds are not. Instead, diamonds are a mineral that helps make up the kimberlite rock.

The same is true for the quartz crystal that is just to the left of the dollar bill. Quartz is a mineral that makes up a large part of many kinds of rocks, but you don't find huge deposits of pure quartz. Quartz is a mineral, but not a rock.

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