CHAPTER 2 MINERALS Group Presentation Notes
DEFINITION OF A MINERAL A mineral is naturally occurring, inorganic solid with an orderly crystalline structure and a definite chemical composition.
CHARACTERISTICS 1. Naturally occurring minerals form by natural geologic processes; not man made 2. Solid substance exists as a solid on Earth s surface
CHARACTERISTICS 3. Orderly crystalline structure atoms are arranged is an organized pattern, which affects their crystal shape (internal structure)
CHARACTERISTICS 4. Definite chemical composition most minerals are chemical compounds of two or more elements. 5. Generally considered inorganic most minerals are inorganic crystalline solids found in nature, like halite (table salt).
WAYS THAT MINERALS FORM 1. Crystallization from Magma as magma cools, elements combine to form minerals Examples: Quartz, Muscovite, Feldspar
WAYS THAT MINERALS FORM 2. Precipitation as water evaporates, the dissolved substances in the water can react to form minerals Examples: Calcite and Halite (limestone caves are formed by this same process)
WAYS THAT MINERALS FORM 3. Pressure and Temperature an increase in pressure and/or temperature can cause minerals to become unstable and recrystallize (atoms rearranged) to form new minerals. Examples: talc and muscovite
WAYS THAT MINERALS FORM 4. Hydrothermal Solutions is a very hot mixture of water and dissolves substances. When existing minerals come in contact, chemical reactions can take place to form new minerals. When solution cools dissolved substances combine to form minerals. Examples: Bornite, chalcopyrite, quartz, and pyrite
HOW GROUPED? Common minerals, together with the thousands of others that form on Earth, can be classified into groups based on their composition.
SILICATES Silicon (Si) and oxygen (O) combine to form a structure called the silicon-oxygen tetrahedron. This tetrahedron can join in a variety of ways affecting the crystal shape. Example: Quartz, micas, augite & hornblende
CARBONATES Minerals that contain the elements carbon (C), oxygen (O) and one or more other metallic elements. Examples: Calcite (CaCO 3 ) and Dolomite
OXIDES Minerals that contain Oxygen and one or more other elements, which are usually metals. Examples: Corundum (Al 2 O 3 ) & Hematite (Fe 2 O 3 )
SULFATES AND SULFIDES Minerals that contain the element sulfur. Examples: Anhydrite, Gypsum, Galena, Sphalerite, and Pyrite.
HALIDES Minerals that contain a halogen ion plus one or more other elements. Examples: Halite (NaCl) & Fluorite (CaF 2 )
NATIVE ELEMENTS A group of minerals that exist in relatively pure form. Examples: Gold (Au), Silver (Ag), Copper (Cu), Sulfur (S), and Carbon (diamond & graphite)
Properties of Minerals
COLOR Unique to some minerals, while others will come in many different colors and several different minerals can come in the same color. Color of minerals come from the elements. Example: Copper and Aluminum give turquoise its blue-green color
STREAK The color of a mineral in its powdered form. Obtained by rubbing a mineral across a streak plate (little piece of unglazed tile). Color of the streak does not vary from sample to sample in the same mineral. Example: Hematite has a distinctive red-brown streak
LUSTER Used to describe how light is reflected from the surface of a mineral. Different types of luster: Metallic, nonmetallic, glassy, pearly, silky, earthy and brillant
CRYSTAL FORM The visible expression of a mineral s internal arrangement of atoms. When a mineral forms slowly and without space restrictions, it will develop into a crystal with well-formed faces
HARDNESS A measure of the resistance of a mineral to being scratched One of the most useful properties in identifying minerals Standard hardness scale called the Mohs scale consists of 10 minerals arranged from 10 (hardest) to 1 (softest)
CLEAVAGE The tendency of a mineral to cleave, or break, along flat even surfaces. Example: Mica cleaves to form flat sheets
FRACTURE The uneven breakage of a mineral. Example: Quartz has a curvy fracture called conchoidal fracture.
DENSITY A property of all matter that is the ratio of an object s mass to its volume. Example: Density of Galena is 7.5g/cm 3
DISTINCTIVE PROPERTIES Distinctive feels: talc feels soapy and graphite feels greasy Some metallic minerals are easily shaped Some minerals like magnetite are magnetic Double refraction: calcite makes printed material appear double Carbonate minerals react with acid (HCl) fizz and bubble Smell: sulfur smells of rotten eggs