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Rocks and Minerals

Lecture Part I: Minerals

mineral

Definite Chemical

Composition

Inorganic

Crystal Structure

Naturally occurring

Solid

Five Properties of Minerals

Did not come from something living

Repeating pattern

Always contains the same elements

Definite volume and shape

Formed by processes in natural world

Over 4,000 minerals exist!

Scientists use 8 different properties to identify

minerals.

color streak luster

density hardness

Crystal type cleavage or fracture

special properties

How do we identify minerals?

1. Color - easily observed but many minerals have the same color.

Which one is the mineral, gold?

Pyrite Gold Chalcopyrite

2. Streak – the color of a mineral’s powder.

Try it: hematite #19 & galena #14

3. Luster – how light reflects on the surface of the mineral.

Metallic Glassy Waxy, Greasy

Dull Silky Earthy

4. DensityThe mass in a given space – how much “stuff” is in the mineral.

The density does not change based on size.

Density = Mass / Volume

5. Hardness – one of the best clues to identify a mineral.

Mohs Hardness Scale (1812) – ranks ten minerals from hard to soft.

A scratch test is used to determine hardness.

6. Crystal Systems – atoms in a mineral grow in a pattern.

7. Cleavage & Fracture

A mineral that splits evenly along flat

surfaces.

A mineral that does not split apart

evenly.

mica talc

8. Special Properties

Some minerals have fluorescence, magnetism,

reactivity to acids, and optical properties.

Minerals are INORGANIC and naturally occurring.

Minerals have a crystal structure with a definite chemical composition.

They are identified by their color, streak, luster, density, hardness, cleavage or fracture, and special properties.

IN SUMMARY…

HOW MINERALS FORM

Pop Quiz

1. What is the difference between a rock & a mineral?2. What are the five characteristics of ALL minerals?3. What are 8 properties used to identify minerals?4. How do you calculate density?5. What is the difference between cleavage & fracture?6. What is the difference between color & streak?7. What is the Mohs Hardness Scale?

The process by which atoms are arranged to form a material with a crystal structure.

geode

Crystallization

Two Ways Minerals Form

1) crystallization of lava or magma, 2) crystallization of materials in

solutions.

Minerals From Magma & Lava

When these liquids cool to a solid state, they form crystals.

Minerals From Solutions

Solution - A mixture in which one substance is dissolved in another.

Minerals Formed by Evaporation

When ancient seas slowly evaporated, minerals formed (halite, gypsum, calcite).

HALITE

Minerals from Hot Water Solutions

Elements that form minerals dissolve in hot water underground; when the solution cools, the elements

crystallize as minerals.

These iron-rich minerals formed at an undersea vent

Pure Metal VeinsA narrow channel of a mineral that is different

from the surrounding rock; usually pure metals.

The Size of CrystalsDepends on the rate at which the magma/lava

cools or the solution evaporates.

Slow Cooling Crystals

Slow cooling leads to the formation of large crystals.

Rapid Cooling Crystals

Magma closer to the surface loses heat energy much faster than magma deep below ground.

Rapid cooling leaves no time for large crystals. Crystals are small.

Minerals form from magma and lava when the hot magma cools inside the crust or the lava hardens on the surface.

Minerals form when elements and compounds are dissolved in water and they leave a solution which eventually crystallizes.

Minerals form when solutions evaporate (Example: halite from the ancient seas and gypsum)

IN SUMMARY…

Preview “minerals an their uses”

Mineral identification using samples. Name of mineral 3 words to DESCRIBE it.

Mineral poster – front side Title: Your mineral In the center draw/print/glue a picture of something that contains your mineral 5 bubbles around the picture in the center that describe the PROPERTIES of

that mineral Minerals Lab Part I: DENSITY (review identification

properties) Analysis: explain the other ways to identify minerals. Make crystals with kit Make your own sugar crystals