CLASSIFYING ROCKS

P. 94-97

4.1

STUDYING ROCKS

GEOLOGISTS LOOK AT SEVERAL CHARACTERISTICS:

1. MINERAL COMPOSTITION 2. COLOR 3. TEXTURE

MINERAL COMPOSTITION

ROCKS ARE MADE OF MIXTURES OF MINERALS AND OTHER MATERIALS. ABOUT 20 MINERALS MAKE UP MOST OF THE EARTH’S CRUST. THESE ARE KNOWN AS THE ROCK-FORMING MINERALS.

COLOR

A ROCKS’ COLOR PROVIDES CLUES AS TO WHICH MINERALS ARE IN THE ROCK.

BASALT- A DARK COLORED ROCK THAT IS LOW IN SILICA

GRANITE- A LIGHT COLORED ROCK HAS HIGH AMOUNTS OF SILICA

REMEMBER COLOR DOESN’T TELL US MUCH.

TEXTURE

VERY USEFUL FOR IDENTIFYING. GRAINS ( PARTICLES OF MINERALS)

GIVE ROCK THEIR TEXTURE OR FEEL AND LOOK OF ROCK’S SURFACE.

SMOOTH, GLASSY, CHALKY, ROUGH, ALSO USE SIZE SHAPE AND

PATTERN OF GRAIN.

GRAIN SIZE

IF A GRAIN IN A ROCK IS LARGE AND EASY TO SEE IT IS CALLED COURSE- GRAINED.

FINE-GRAINED IS SO HARD TO SEE YOU WOULD NEED A MICROSCOPE.

\SOME HAVE NO VISIBLE GRAIN EVEN UNDER A MICROSCOPE.

GRAIN SHAPE

SOME GRAINS ARE ROUNDED AND SOME ARE JAGGED.

GRAIN PATTERN

SOME GRAINS FORM PATTERNS. THEY CAN LIE IN FLAT LAYERS OR

STACKS . SOME SWIRL. SOME HAVE DIFFERENT COLOR BANDS.

BANDED/ NONBANDED.

HOW ROCKS FORM

WE WANT TO DETERMINE A ROCK ORIGIN. WE CLASSIFY ROCKS INTO CATEGORYS BASED ON WHERE THEY FORMED.

IGNEOUS- MAGMA OR LAVA METAMORPHIC-HEAT/PRESSURE SEDIMENTARY-CEMENTED/

COMPACTED/BURIED

What are minerals made up of and how do they

form?

3.2 p. 76-79

What are minerals made up of?

Minerals are made up of elements or compounds. Elements are atoms that are all alike and have the same number of protons, neutrons, and electrons. Some minerals are compounds which are combinations of different elements.

Reminder atoms have a nucleus and an electron cloud.

The atom

Protons and nuetrons are in the nucleus. Electrons are in the electron cloud.

Mineral crystals

I know that it is a stretch to get from atoms to minerals but minerals are made up of tiny atoms and when they bond together- they form minerals. They also form into 6 particular shapes or patterns.

Cubic, hexagonal, etc

Crystallization

Crystal come in many sizes. Some are geodes which are a rounded hollow rock lined with mineral crystals.

They form when water seeps into the rock and slowly evaporates leaving the minerals behind to crystallize. Crystallization is the process by which atoms arrange themselves into a pattern.

2 ways minerals cystallize

1. from molten material 2. from being dissolved in water

Minerals from magma and lava

Magma-molten material inside the earth Lava- magma that reaches the surface. Anytime magma cools whether inside the

Earth or as lava, minerals crystallize. The size of the crystals depend on the rate of cooling.

Cools slow- large crystals Cools fast- small crystals

Minerals from solutions

A solution is a mixture in which one substance is dissolved into another substance.

Mineral crystals can form this way underground or in bodies of water on Earth’s surface either by evaporation or from hot water solutions.

Evaporation

When minerals are left behind after water evaporates then crystals form

Examples: Halite Gypsum calcite

Hot water solutions

Magma heats water underground and causes minerals to dissolve in the water, when this water cools the elements and compounds leave the solution and crystallize.

Pure metals form veins or narrow chambers or slabs of minerals. They often form in cracks in the rock surrounding it.