Minerals

What is a mineral? A mineral is a naturally occurring,

inorganic solid with an orderly crystalline structure and a definite chemical composition

5 Characteristics of Minerals 1. Naturally occurring- forms by natural geologic

processes, synthetic gems are not considered minerals 2. Solid Substance- within temperature ranges that

occur at Earth’s surface 3. Orderly crystalline Structure- atoms are arranged

in an orderly and repetitive manner 4. Definite Chemical Composition- minerals are

chemical compounds made up of a two or more elements (exception- native elements)

5. Generally Considered Inorganic- table salt is inorganic, sugar is organic and is not a crystal. Sugar comes from a plant Calcium carbonate- secreted by marine animals, inorganic

or organic?

How do minerals form? Four major processes by which minerals

form 1. Crystallization from magma 2. Precipitation 3. Pressure and Temperature 4. Hydrothermal Solutions

Crystallization of Magma Magma is molten rock that occurs

deep within the Earth As magma cools, elements combine

to form minerals First minerals formed are rich in

iron, calcium, magnesium Next are minerals rich in sodium,

potassium, and aluminum

Precipitation Minerals form when water evaporates in

lakes, rivers, ponds, and oceans Minerals are left behind or precipitated

from the water Halite and calcite form this way

Pressure and Temperature Some minerals from when others are

subject to changes in pressure and temperature

Atoms are rearranged to form more compact minerals

Talc and muscovite are formed this way

Hydrothermal Solutions Hydro (water) thermal (heat) Very hot mixtures of water and

dissolved substances Can have temperature between

100oC and 300oC Chemical reactions occur at these

temperatures causing minerals to form, or as solution cools minerals form

Mineral Groups There are over 3800 named minerals on

Earth and more are identified each year Common Minerals are classified into

groups based on their composition Seven mineral groups-

Silicates, carbonates, oxides, sulfates, sulfides, halides, native elements

Silicates These are the most common- remember from

chemistry unit, the most abundant elements in Earth’s crust are oxygen and silicon

Silicon-oxygen tetrahedron- structure which consists of one silicon to four oxygen molecules (most silicates occur in this form)

Most silicate minerals form from crystallization of magma near or far below earth’s surface

Examples include- quartz, augite, micas

Carbonates Second most abundant mineral group

Contain carbon, oxygen, and one or more other metallic elements

Examples include calcite, dolomite, limestone, marble

Oxides Oxides contain oxygen and one or more

other elements, which are usually metals

Some form under Earth’s surface from crystallization of magma (rutile), others from when minerals are subject to changes in temperature and pressure (corundum), others form when a mineral is exposed to liquid water (hematite, iron oxide)

Sulfates and Sulfides Both contain sulfur Sulfates- (anhydrite, and gypsum) form

when mineral rich waters evaporate Sulfides- (galena, sphalerite, pyrite)

form from hydrothermal solutions

Halides This group contains a halogen ion plus

one or more other elements Halogens occur in group 17 (7a) of the

periodic table Examples include- halite and fluorite

Native Elements This group occurs in pure elemental

form Examples include- gold, silver, copper,

sulfur, carbon (graphite and diamonds)

Properties of Minerals and Mineral Identification Properties of minerals are determined by composition

and structure Color Streak Luster Crystal Form Hardness Cleavage Fracture Density Unique properties include- magnetism, double refraction,

chemical reactions with HCl

Color and Luster Color can be unique to some minerals, but

for most it is not the most useful for identification Color within minerals can vary depending on

other elements present within the mineral Luster- how light is reflected from the

surface of a mineral Metallic (metal like), vitreous/glassy

(quartz), pearly, silky, earthy

Streak and Crystal Form Color of a mineral in its powdered form We can use a streak plate (a sheet of unglazed

porcelain) to determine this property Crystal form- visible expression of internal

arrangement of atoms When a mineral forms without any space

restrictions it will develop into a perfect crystal with well developed faces

6 Crystal Forms

Type 1: Isometric (Cubic) 6 sides All sides are

square Examples

*pyrite*halite*diamond*galena

Type 2: Tetragonal6 sides4 rectangles, 2

squares (right angles)

Example*zircon

Type 3: Hexagonal8 sides2 hexagons, 6

rectangles (right angles)

Examples*ice*quartz*emeralds

Type 4: Orthorhombic6 sides6 rectangles (3

pairs of rectangles with different sizes at right angles)

Examples*topaz*barite

Type 5: Monoclinic6 sides4 rectangles, 2

parallelograms (several angles)

Examples*gypsum*muscovite

Type 6: Triclinic6 sidesParallelograms

(no right angles)Example

*turquoise

Mineral with a Cubic or Isometric Crystal Shape

Pyrite has a Cubic Crystal Structure

Mineral with a Tetragonal Crystal Shape

Rutile has a Tetragonal Crystal Structure

Mineral with a Hexagonal Crystal Shape

Ruby has a Hexagonal Crystal Structure

Minerals with Orthorhombic Crystal Shapes

The is a very big crystal system containing gemstones such as topaz, peridot, tanzanite, and many others

Mineral with a Monoclinic Crystal Shape

Gypsum is a mineral with a Monoclinic Crystal Structure

Mineral with a Triclinic Crystal Shape

Calcite- Triclinic crystal look like a rectangular box that someone pushed from one side to make it lean

Hardness One of the more useful properties for

identification Done by rubbing two minerals together,

one will scratch the other unless they have the same hardness

Mohs Hardness Scale- 1-10 Talc is the softest, what is hardest?

Moh’s Hardness Scale

Cleavage and Fracture Cleavage is the tendency of a mineral to

cleave or break along flat, even surfaces Fracture is what happens to all other minerals

that do not display cleavage Fracture can be described as the uneven

breakage of a mineral

Internal atomic structure determines whether a mineral will display cleavage or fracture

Fracture or Cleavage?

Selena

Density Ratio of an objects mass to its volume D= M/V For minerals we would use g/cm3, since

we are looking at solids Density of pure minerals are of

constant value. Therefore we can use density to identify pure minerals or to tell if a mineral is not in pure form.

Other Properties Magnetism- some types of magnetite are

magnetic and can be used to pick of metal objects

Double Refraction- When calcite is placed over printed words the letters appear doubled

Chemical Reactions with HCl- Carbonate minerals will fizz when they come into contact with hydrochloric acid

Double Refraction of Calcite

Magnetism