rocks

what are rocks

A rock is a naturally formed, non-living Earth material. Rocks are made of collections of mineral grains that are held together in a firm, solid mass (Figure 1.1). How is a rock different from a mineral? Rocks are made of minerals. The mineral grains in a rock may be so tiny that you can only see them with a microscope, or they may be as big as your fingernail or even your finger (Figure Rocks are identified primarily by the minerals they contain and by their texture. Each type of rock has a distinctive set of minerals. A rock may be made of grains of all one mineral type, such as quartzite. Much more commonly, rocks are made of a mixture of different minerals. Texture is a description of the size, shape, and arrangement of mineral grains. Are the two samples in Figure 1.3 the same rock type? Do they have the same minerals? The same texture? The different colors and textures seen in this rock are caused by the presence of different minerals. A pegmatite from South Dakota with crystals of lepidolite, tourmaline, and quartz (1 cm scale on the upper left). Sample 2 Crystals are tiny or microscopic Magma erupted and cooled quickly Andesite As seen in Table 1.1, these two rocks have the same chemical composition and contain mostly the same minerals, but they do not have the same texture. Sample 1 has visible mineral grains, but Sample 2 has very tiny or invisible grains. The two different textures indicate different histories. Sample 1 is a diorite, a rock that cooled slowly from magma (molten rock) underground. Sample 2 is an andesite, a rock that cooled rapidly from a very similar magma that erupted onto Earths surface. A few rocks are not made of minerals because the material they are made of does not fit the definition of a mineral. Coal, for example, is made of organic material, which is not a mineral. Can you think of other rocks that are not made of minerals? Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL:

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instructional diagrams

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questions

which one of these is not a description of texture?

a) size

b) shape

c) arrangement of mineral grains

-->  d) color

a rock made of grains that are so tiny they cannot be seen without a microscope is a rock, but it is not made of minerals.

a) true

-->  b) false

how does diorite differ from andesite?

a) different minerals are present.

b) very different colors.

-->  c) crystal size.

d) composition of magma they cooled from.

not all rocks contain grains that fit the definition of a mineral.

-->  a) true

b) false

two different rock types must always different in their

-->  a) composition

b) texture

c) both composition and texture.

d) composition and texture, or composition or texture.

rocks are identified primarily by

-->  a) their minerals and texture

b) the size and shape of their minerals

c) their color

d) the arrangement of their mineral grains

_____ is a naturally formed, non-living earth material.

-->  a) rock

b) coal

c) fossil

d) concrete

which one of these rocks does not contain minerals?

a) diorite

b) granite

-->  c) coal

d) pegmatite

diorite is a rock cooled from

a) lava

-->  b) magma

c) metamorphic rocks

d) the core

the difference between diorite and andesite is

-->  a) andesite cooled from erupted magma and diorite cooled from magma underground

b) both rocks cooled from erupted magma

c) both rocks cooled from magma underground

d) andesite cooled from magma underground and diorite cooled from erupted magma

diagram questions

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