Minerals

A mineral is a naturally occuring, inorganic, crystalline solid with a specific chemical composition.

NATURAL

Minerals are created by the Earth itself…not from human

influence.

INORGANIC

Minerals are not made by living things or are composed of living

things.

CRYSTALLINE

The arrangement of atoms within a mineral creates a crystalline structure. Each mineral has its own unique

structure.

CHEMICAL COMPOSITION

Minerals are composed of one element or many

elements in the form of a compound.

Chemical Composition of Minerals

Some minerals are composed of a single

element.

Ex: Sulfur = S

Some minerals are composed of a combination of

elements known as a compound.

Ex: Fluorite = CaF2

(combination of calcium and fluorine)RT = Pg. 16

Crystalline Structure of Minerals

The atoms with a mineral are arranged and bonded in a specific way creating the crystalline structure of the

mineral.

The crystalline structure of a mineral helps to determine that mineral’s physical and chemical properties – such as

hardness and cleavage.

The majority of the Earth’s crust (by mass and volume) is made up of the elements oxygen and

silicon. The “silicon-oxygen tetrahedron” is the basic

building block of many minerals.The arrangement of silicon-oxygen tetrahedrons determines the crystalline structure of minerals.

Rock vs. MineralA rock is a naturally formed solid that is part of the

Earth.

All minerals are rocks, but not all rocks are minerals.

Most rocks are composed of one or more minerals. Some rocks are composed of glassy or organic

materials

COAL

Coal is composed of the organic remains of ancient plant and

animal matter (organic).

Minerals are inorganic.

OBSIDIAN

Obsidian is volcanic glass that is formed by heated rock being cooled very quickly. Glass has a

noncrystalline atomic structure.

Minerals have a crystalline structure.

Mineral Properties and Identification The best method for

mineral identification is through the use of X-ray

diffraction.

A beam of X-rays passing through a

mineral sample will diffract leaving a unique

“x-ray pattern” on photographic film.

Each mineral has its own unique diffraction

pattern.

Minerals have a unique set of physical and chemical properties that reflect its internal arrangement of atoms.

When in the field, scientist will use other methods to identify minerals.

Mineral Properties and Identification Color

The color of a mineral can be used for identification in some cases. Many times minerals will change due to impurities found within the rock

or mineral.

Color is NOT a reliable mineral property used in identification

SULFURSulfur is well known for

its yellow color.

QUARTZAll three samples are of

the same mineral. In this case color would not be useful tool in mineral

identification.

Mineral Properties and Identification Streak

The residue of a mineral left on a scratch plate is known

as streak.

The streak color does not always match the color of

the mineral.

The streak of a mineral is more consistent than the

color of a mineral and, therefore, is a more reliable

test for mineral identification.

HEMATITEHematite is a silver colored mineral.

When scratched on a porcelain plate, its streak is reddish-brown.

Mineral Properties and Identification Luster

The shine from an unweathered mineral in light is known as luster.

Minerals may have metallic or nonmetallic lusters.

A mineral with a metallic luster shines like a metallic surface (Ex: clean steel pot).

Most minerals have a nonmetallic luster.

PYRITEPyrite has a metallic luster and

shines like a metallic surface in the light.

OLIVINEOlivine does not shine like a metallic

surface in the light. It has a nonmetallic luster.

Mineral Properties and Identification Hardness

The resistance to being scratched is known as a mineral’s hardness.

Moh’s Hardness Scale is a tool used by scientists to determine the hardness of a mineral. Scientists can determine whether an unknown mineral can “scratch” or be “scratched” by known common materials.

This will help a scientist determine the hardness of an unknown mineral.

Gypsum has a hardness of 2 and calcite has a harness of 3. A

fingernail has a hardness of 2.5. A fingernail can “scratch”

gypsum and “be scratched” by calcite.

Mineral Properties and Identification Cleavage

The tendency of a mineral to break along a zone of weakness

is known as cleavage.

Zones of weakness found within a mineral relate to the

crystalline structure of the mineral.

Sometimes zones of weakness can be seen as smooth sides

with a luster.

Minerals that lack zones of weakness will break or “cleave” along uneven surfaces. This is

known as fracture.

MUSCOVITE MICA

GALENA

CLEAVAGE:Zones of weakness

FRACTURE:Uneven brake

Mineral Properties and Identification

Other Tools for Mineral Identification

Specific Gravity

Specific gravity is the density of a

mineral compared to that of water.

Crystal Shape

The geometric shape a mineral

takes is known as crystal shape.

Reaction with HCl acid

Certain minerals will react in the presence of hydrochloric acid.