What are minerals? A mineral is a naturally occurring, solid, inorganic substance that has definite chemical composition and structure. Naturally occurring means not produced artificially. Inorganic means that it does not contain carbon from a living source.

The Back Page of the ESRT is Devoted to Minerals This chart is used to identify samples of minerals This is a key activity for the lab practical exam, which counts for 15% of your regents grade. The lab practical is given in the last week of classes in June. The other 85% is from the exam.

Mineral Characteristics Minerals are classified on the basis of Physical properties Three dimensional structure Chemical composition Chemical properties The Properties of Minerals on your ESRT has information on all of these.

Physical Properties of Minerals Mineral identification is usually accomplished by studying their physical properties. Minerals have six important physical properties that are commonly used… Color Streak Luster Hardness Cleavage Fracture

Color Color is the most visible properties of a mineral. The use of color is problematic for several reasons… Many minerals exhibit the same color One of these gems is a diamond, the other a ruby. Which one is which? Many minerals are found in a variety of colors

All of these samples are quartz, SiO2

Mineral colors are often caused by impurities: metallic element from the middle of the periodic table…

Streak Streak is the color of a mineral in its powdered form. A mineral’s streak may be different than its outward appearance. Streak is more reliable than color for mineral identification.

Luster Luster is the way light is reflected from the surface of a mineral. Luster can be metallic or non-metallic. Minerals with metallic luster shine like polished metals. Minerals with non-metallic luster have no metallic shine. There are several different non-metallic lusters… Glossy, pearly, greasy, dull, earthy

Hardness The hardness of a mineral is its resistance to being scratched. The hardness of a mineral is determined by comparing it to the hardness of reference minerals (Moh’s Hardness Scale)

Cleavage Cleavage is the tendency of a mineral to split along one or more smooth surfaces, or planes. There are several common types of cleavage. Mica splits in one direction, halite (salt) cleaves in three directions.

Fracture Minerals that do not show cleavage are said to fracture when they break. The fracture of most minerals is uneven (rough) Your ESRT has columns for cleavage and fracture

Other Properties of Minerals Magnetism Taste Double refraction Reaction with acid (a chemical property) These are also shown on reference table

Formation of Minerals Minerals form under three circumstances: In loose cavities Attached to a wall of rock surrounding a cavity Embedded in a rock

Herkimer “Diamonds” Herkimer, New York

Crystals All minerals are crystalline – composed of atoms arranged in a pattern. Crystals are minerals with geometric shapes and smooth, flat surfaces called faces. Each mineral has its own crystal shape. When a mineral has room to form without restrictions, it will develop individual crystals. There are 6 basic crystal systems

Origin of Minerals Minerals begin a supersaturated solutions. As water evaporates, atoms or ions collect together and precipitate out. The speed of evaporation determines the size of the crystals – the slower the rate, the larger the crystals. Minerals can form as a result of cooling and solidification of magma Minerals can form as a re- arrangement of atoms in existing minerals under high temperature and pressure. Origin of Minerals

Chemical Composition Minerals are grouped according to their chemical composition. All minerals are made of elements. Some minerals can be identified by their special chemical properties

Graphite vs. Diamond Both made of carbon atoms, with very different properties. Graphite is soft and diamond is very hard.

Cleavage is a function of chemical structure Minerals split along planes where the bonds between layers are weak. Halite with weak layers between layers splits into cubes. Quartz does not split (fracture) because all bonds are strong.

Some minerals are made up of just one element

Most minerals are compounds – 2 or more elements

Which minerals are silicates? Other common classes of minerals include carbonates, sulfides, and iron oxides.

Mineral Composition Most minerals are composed of eight common elements found in the earth's crust. Your reference table shows the percent by volume and mass for these eight elements: Note that two elements, oxygen and silicon, make up most of the mass of the crust. These elements combine to form minerals called silicates.

Silicates

Silicates Reading

Lab 22 Mineral Identification

Other Characteristics ID Luster (M or NM) Hardness Cleavage/ Fracture Color Other Characteristics Mineral Name A   B C D E F G H I J K L M N O