Chapter 4 Notes:

Common minerals that make up most of the rocks in Earth's crust are called Rock-forming Minerals

The study of minerals and their properties is called Mineralogy

Identification of Minerals

• Color is the first to be observed. It is the least useful test since most minerals do not show their true color due to oxidizing or impurities.
• Luster of a mineral is the way the mineral shines in reflected light. Luster is either metallic or non-metallic.

1. vitreous - like shining glass
2. pearly - like a pearl
3. resinous - wax or dull glassy shine
4. others include: greasy, oily, dull, or earthy

• Crystal shape is sometimes helpful in identifying a mineral. Many minerals have differing crystal shapes
• The Streak of a mineral is the color of its powder. For many minerals, the streak is not the same as its visible color. Ex - Pyrite is gold in color but its streak is black.
• The Cleavage of a mineral is its tendency to split easily or to separate along flat surfaces.
• When minerals break along other than cleavage surfaces, they are said to have Fracture.
• The Hardness of a mineral is its resistance to being scratched. Diamond is the hardest of all minerals.
• Hardness was developed by Friedrich Mohs - he ranked all minerals on a scale of 1 to 10 as shown in the chart:

Mohs Scale:

Hardness - Mineral - Simple Test

1 Talc Fingernail can scratch it

2 Gypsum Fingernail can scratch it

3 Calcite Copper penny will scratch it

4 Fluorite Knife needed to scratch it

5 Apatite Knife needed to scratch it

6 Feldspar It will scratch glass

7 Quartz Hardest common mineral

8 Topaz Harder than any common min.

9 Corundum Scratches topaz

10 Diamond Hardest of all minerals

The Acid Test

• Calcite is the principal mineral in limestone and marble. Calcite is calcium carbonate, so a drop of weak hydrochloric acid will cause the calcite to fizz, giving off carbon dioxide.

Other Tests

• Magnetism can be identified in magnetite
• Taste can be identified in halite (rock salt)
• Fluorescence is the state of glowing while under ultraviolet light. Like in fluorite and calcite
• Phosphorescence is the ability to stay glowing after the ultraviolet light is turned off. Like in willemite and sphalerite
• Some minerals like uranium are radioactive and can be detected using a Geiger counter.
• Other minerals like calcite have double refraction, which causes the light that shines through them to split in two. Causes you to "see double" while looking through the mineral.

The Silicates

• A group of minerals with silica as their major component
• Quartz (silicon dioxide) is the hardest common mineral known - #7 on Moh's scale. It is the second most abundant mineral in earth's crust.
• Feldspar is the name of the most abundant family of minerals in earth's crust. All have two directions of cleavage; #6 on Moh's scale; and pearly luster.
• Mica is a mineral found in soft rocks. It cleaves almost perfectly in one direction
• Talc is the softest of all minerals - #1 on Moh's
• Hornblende is a shiny, dark green and cleaves in 2 directions - #5-6 on Moh's scale

The Carbonates

• A carbonate mineral is made of carbonate groups joined with carious metal ions.
• Limestone (rock) is made of carbonate mineral
• Marble (rock) is made of carbonate mineral
• The most common carbonate is calcite (calcium carbonate) - #3 on Moh's scale
• Iceland spar is a type of calcite that is double refractive and transparent
• Dolomite is calcium magnesium carbonate and is commonly found in limestone and marble
• Others include the popular Malachite (green) and Azurite (blue) which have unique colors

The Iron Oxides

• Minerals that contain large amounts of Iron
• Irons tend to combine with oxygen or sulfur to form an oxide or sulfide.
• An oxide is a mineral consisting of a metal element combined with oxygen
• A sulfide is a metal element combined with sulfur
• Hematite is the most common iron oxide; most is reddish in color and #6 on Moh's scale
• Magnetite is a black magnetic iron oxide; #5.5 on Moh's scale; Lodestone is a highly magnetic variety of magnetite
• Pyrite is iron sulfide and is gold in color; referred to as "fool's gold" because the average person will not tell it from real gold. It does however have a much harder composition - #7 on Moh's scale