Minerals

Minerals

Multiple Choice

A geologist is comparing the properties of different minerals. He rubs each one on a piece of white tile and observes the color of the powder that is left behind. What type of test did he perform?

• color

• hardness

• luster

• streak

​Explanation

• ​The streak of a mineral is the color of its powder and is a way to identify different minerals. Hardness is judged by scratching other minerals. Luster is the amount of light that is reflected by the surface of the rock. Remember that when a rock is rubbed on the ground, it leaves a streak of color behind. This is how a streak test is performed.

Multiple Choice

Any mineral can scratch any other mineral ______ than itself.

• heavier

• cleavable

• softer

• harder

Multiple Choice

A mineral can be scratched by another mineral that is __________ than itself.

• heavier

• harder

• softer

• fracture

​Explanation

• ​Any mineral can scratch any other mineral that is softer than itself and can be scratched by any mineral harder than itself. The Mohs hardness scale ranks minerals from soft to hard, and this characteristic is one way of identifying minerals.

Multiple Choice

Stephan’s mother is a mineralogist, and sometimes she brings home samples to study. Stephan observes and compares these minerals. He knows minerals form in several ways. He is especially interested in the minerals that form from volcanic activity and the kinds of crystals they form.

What determines crystal size in minerals formed by lava or magma?

• the kind of mineral that formed

• the amount of material available

• the rate at which the minerals cooled

• the materials in the lava or magma

​Explanation

• ​The correct answer is “the rate at which the minerals cooled.” Crystal size in mineral formation depends on the rate of cooling of lava or magma. The materials on the surface or up high in the crust cool faster with little time for crystals to grow, creating small crystals. Lava and magma that cool slowly tend to form large crystals. The amount of materials do not affect crystal size, nor does the kind of mineral forming.

Multiple Choice

What causes the differences in the way diamonds form compared to graphite?

• high temperature and high pressure

• low temperature and location deep in the mantle

• high pressure and location in the continental crust

• low temperature and low pressure

​Explanation

• ​The correct answer is “high temperature and high pressure.” Diamonds are formed deep in the mantle, with high temperatures and high pressure. The extreme pressure and temperatures alter the graphite and form diamonds. The depth is part of what causes the structural changes.