Mineral Characteristics

• The chapter covers the characteristics of minerals and rocks
• The chapter is organized into three sessions: the first on mineral characteristics, the second on physical properties of minerals, and the third on rock characteristics, types, classifications, and forming processes

Session 1: Characteristics of Minerals

• Minerals and rocks are the main earth materials of interest to geologists
• To be classified as a mineral, a material must be solid, naturally occurring, inorganic, have a definite chemical formula, and have an ordered atomic structure (crystalline)

Solid State

• A mineral must be in a solid state, not a gas or liquid
• Ice in a glacier is a mineral because it is solid H₂O, but liquid water is not
• Natural gas and petroleum are not minerals because they are not solid

Natural Occurance

• Minerals must occur naturally and not be manufactured
• Steel is not a mineral because it is not naturally occurring
• Ice cubes in a refrigerator are not minerals, but a natural glacier is

Inorganic Composition

• Minerals must be formed by non-living processes and not contain organic carbon-based molecules
• Sugar is not a mineral because it is sourced from sugarcane plants
• Natural gas, petroleum, and coal are not minerals because they are formed from once living organisms

Chemical Formula

• The composition of a mineral is defined as the chemical composition of its unit cell
• Quartz has a chemical formula of SiO₂
• Calcite has a formula of CaCO₃
• Halite (table salt) has a formula of NaCl

Ordered Atomic Structure

• Minerals have a highly ordered atomic arrangement of atoms in regular 3-D geometric patterns
• Crystalline materials possess ordered atomic patterns
• Crystals are held together by interatomic forces (chemical bonds)

Mineral Formation

• Minerals are formed through several ways
• From molten rock material (magma or lava), can yield minerals like quartz, olivine, feldspars, and biotite
• Precipitation from hot water associated with magma in hydrothermal veins can yield minerals like pyrite and chalcopyrite
• Precipitation from sea or lake water due to evaporation can yield minerals like halite and gypsum
• Organisms constructing shells can yield minerals like calcite and quartz
• During metamorphism can yield minerals like garnet and muscovite

Session 2: Distinguishing Physical Properties of Minerals

• Physical properties visible by the naked eye can distinguish minerals
• Properties include color, luster, streak, density, hardness, and special properties
• Luster is the shining degree

Color

• Color is often the first and most easily observed physical property of a mineral
• Some minerals always have the same color
• Other minerals can exhibit different colors depending on the environment and impurities merged in them during formation
• Example of a mineral with the same color is malachite, which is always green
• Quartz, can come in transparent, pink, green, purple, or white

Luster

• Luster refers to the general appearance of a mineral surface in reflected light

• Some minerals have metallic luster, like gold

• Minerals like halite (table salt) have glassy luster,

• Luster can be metallic, glassy, or fibrous

• Calcite has a glassy luster

• Gold has a metallic luster

• Chrysotile has a silky luster

• Amber has a resinous luster

Streak

• Streak of a mineral is the color of a finely powdered mineral
• Streak is determined by rubbing the mineral on a piece of unglazed porcelain
• Streak is sometimes completely different from the apparent color of the tested mineral
• The streak of pyrite (fool's gold) is black, while real gold's streak is golden because pyrite contains iron and sulfur

Density

• Density is the amount of matter in a given space (Mass/Volume)
• Pyrite's density is around 5 g/cm³, while gold's density is around 19 g/cm³
• If you have similar volumes of pyrite and gold, gold will be much heavier than pyrite

Hardness

• Hardness of a mineral is its scratching ability and is measured by Moh's scale

• The Mohs hardness scale ranges from 1 to 10

• Diamond, is the hardest mineral that hardness is 10

• Talc, is the weakest mineral hardness of 1

• To identify the harness degree on Moh's scale, we scratch the tested mineral with the minerals included in Moh's scale pack in the laboratory

• Mineral resistance to scratching is also called scratch ability

• Hardness basic tools are Fingernail > 2, Penny 3, Steel of a pocket knife ~5, Steel of a file 6.6, and Quartz crystal 7

Special properties

• Magnetite's characterized by Magnetism
• Fluorite's distinguished by Glowing under ultraviolet light
• Halite (table salt) is notable by its salty taste
• Sulfur is notable by its Smell
• Calcite is remarked by its reaction to light acids, Calcite can dissolve gradually it contact with acid rain

Economic Importance

• Minerals are the main earth materials that enter almost all daily uses
• Dimension stones include Granite (Quartz & Feldspar)
• Building materials include Gypsum and Limestone (Calcite) in bricks, plaster and cement Marble
• Industrial substances include Dolomite & Olivine, Iron & Nickel in steel manufacturing as well as Petrochemical industries
• Glass is derived from quartz & plagioclase, & Copper and Aluminum
• Precious minerals (Gemstones) include Gold, and Platinum
• Ornamental materials include Fluorite, Peridot, Citrine, and Desert rose (gypsum)
• Tourmaline, Beryl, and Halite (table salt) are used as food
• Medical substances: e.g. Aluminum, potassium, apatite, calcite

Session 3: Rocks

Rocks Origin

• Rocks come from one or more different minerals that have been solidified and cooled, cemented together, or squeezed and heated

Rock Composition

• Rocks are materials made of one or more different minerals
• Halite (table salt), is a rock made of only one mineral
• Halite is a mineral and a rock
• Granite, is a rock made up of different minerals

Differences between Minerals and Rocks

• Minerals are solids and naturally occurring
• Rocks are solid and naturally occurring
• Minerals are inorganic
• Rocks can be inorganic or organic with some organic parts like fossils
• A mineral always has the same chemical composition
• Rock composition can differ from location to location with no specific chemical composition
• Rocks do not have an identified shape and have no nutritive value for the human body

Rock Types

• There are three types of rocks: igneous, sedimentary, and metamorphic

Igneous Rocks

• Igneous rocks form from hot magma or lava

• They are classified as either extrusive (volcanic) from lava or as intrusive (plutonic) from magma

• Extrusive rocks cool quickly resulting in small grains, while intrusive rocks cool slowly resulting in large grains

• Origin Below the surface creates Intrusive (plutonic) igneous rocks from magma with the slow rate of cooling creates Granite

• Origin Above the surface creates Extrusive (volcanic) igneous rocks from lava with the fast rate of cooling creates Basalt

• Magma can come to form an igneous rock on the surface of the earth as an extrusive igneous rock

• Magma can remain under the surface of the earth where it crystallizes to form a plutonic or intrusive igneous rock

Sedimentary Rocks

• Sedimentary rocks made if fragments of previously existing rocks
• Sedimentary rocks are classified into mechanical (clastic), chemical, and organic sedimentary rocks
• Mechanical (clastic) sedimentary rocks are made of fragments of previously existing rocks
• Chemical sedimentary rocks are formed by inorganic precipitation or evaporation
• Organic sedimentary rocks come from organisms

Metamorphic rocks

• Metamorphic rocks form where rocks are changed because of temperature and/or pressure

• The parent rock can be sedimentary, igneous, or another metamorphic rock

• Changing rocks occurs in volcanic or tectonically active areas

• Marble is a metamorphic rock that was originally limestone subjected to heat (temperature)

• Quartzite is a metamorphic rock that was created when sandstone was subjected to changing conditions

• Metamorphic rocks are either foliated or nonfoliated

• Foliated rocks form under high pressure and temperature and have parallele mineral alignment

• Examples include Schist and Gneiss

• Nonfoliated rocks are not banded, and they do not break into layers

• Examples include Marble and Quartzite