Identifying minerals

(with slides from ‘duncanpatti’ and ‘ms. Wells’)

A mineral:

1. Occurs naturally (not man-made) 2. is a solid 3. is a chemical compound arranged in

an orderly pattern (crystals) 4. is inorganic (not made from dead

plants or animals) 5. Is an element or a compound

What are minerals?

Properties of Minerals:Which are the most important?

• Streak• Luster• Cleavage or Fracture• Density• Hardness

Physical Properties of Minerals (can be used to identify the mineral)

Color• Can be misleading• Can vary with the type of impurities

Physical Properties of Minerals (can be used to identify the mineral)

Luster• Surface

reflection • metallic = shiny

like metal• non-metallic =

dull, non-shiny surface

Pyrite has a metallic luster

Calcite has a non-metallic luster

Metallic Luster

Nonmetallic Luster

Physical Properties of Minerals (can be used to identify the mineral)

Streak• The color of the powdered

form of the mineral• The color of the streak can be

different than the mineral• Minerals must be softer than

the streak plate

Streak…can help identify quartz

http://www.childrensmuseum.org/geomysteries/cube/b3.html

Breaking Properties:Cleavage or Fracture

• Cleavage – mineral breaks along a flat surface or into sheets

• Fracture – when a mineral breaks with lots of jagged edges

Hardness = resistance to scratching Hardness does not concern

brittleness (brittle = breaks apart easily)

e.g. glass is brittle (breaks easily when dropped), but it is harder than copper, i.e. it can scratch copper.

copper cannot scratch glass

Mineral test #1: hardness

Physical Properties of Minerals (can be used to identify the mineral)

Hardness• How easily a mineral scratches

materials• Mohs Hardness Scale

• Scale from 1 (softest) to 10 (hardest)• Test by seeing if the mineral can scratch

different objects (like human fingernail, copper, penny, glass, steel file)

Talc(Mg3Si4O10(OH)2)

Gypsum (CaSO4·2H2O)

Calcite CaCO3

Fluorite CaF2

Apatite Ca5(PO4)3(F,Cl,OH)

Feldspar KAlSi3O8 - NaAlSi3O8 - CaAl2Si2O8

Quartz SiO2

Topaz Al2SiO4(F,OH)2

Corundum Al2O3

(do you really need a picture?)

Diamond

cleavage: tendency of a mineral to split easily or separate along flat surfaces

e.g. mica: 1 cleavagefeldspar: 2 cleavagescalcite: 3 cleavagesgalena: 3 cleavages

Mineral test #2: cleavage

Physical Properties of Minerals (can be used to identify the mineral)

Cleavage & Fracture• The way the mineral breaks• Cleavage—minerals break

along smooth, flat surfaces and every fragment has the same general shape• Fracture—minerals that

break at random with rough or jagged edges

Cleavage or Fracture?

1.

4.

3.

2.

Specific gravity: “how dense is the mineral compared to water?”

Nearly all minerals are denser than water.

Mineral test #3: specific gravity

If a mineral is denser than water, its specific gravity is greater than 1.

If it is less dense than water, its specific gravity is less than 1.

If it is equally dense as water, its specific gravity equals 1.

specific gravity, cont’d

Extra Special Properties

1. Fluorescence• Fluorescent color under ultraviolet (UV)

light2. Magnetic• Attract magnets

3. Acid reaction• Carbon dioxide gas bubbles off when

you drop acid on them• Carbonates!

Fluorescence

Magnetic

Carbonate Acid Reaction