MINERALS

Minerals must have four characteristics: ▪ it must be inorganic—not made of or by living things; ▪ it must occur naturally—it cannot be man-made; ▪ it must be a crystalline solid; ▪ it must have a consistent chemical composition.

 10 are so common that they make up 90% of Earth’s crust.  quartz, orthoclase, plagioclase, muscovite, biotite, calcite, dolomite, halite, gypsum, and ferromagnesian minerals.  Two main groups:  silicate minerals  nonsilicate minerals

 Contain silicon and oxygen, and possibly one or more metals  Common silicate minerals  quartz, feldspars, micas,and ferromagnesian minerals, such as amphiboles, pyroxenes, and olivines.  Make up 96% of Earth’s crust.  Quartz and feldspar alone make up more than 50% of the crust.

 No silicon and oxygen compounds  Make up about 4% of Earth’s crust.  Six major groups based on their chemical compositions  carbonates, halides, native elements, oxides, sulfates, and sulfides.

 Each type of mineral is characterized by a specific geometric arrangement of atoms, or its crystalline structure.  A crystal is a solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern

 Silicon-Oxygen Tetrahedron- basic unit of the structure of silicate minerals. Si +4 and 4 O -2  Ex: Olivine  Ex: Beryl and tourmaline

 Ex: Pyroxenes  Ex: Amphiboles

 Ex: Biotite and muscovite

 Ex: Quartz and feldspar

 Diverse chemical compositions = vast variety of crystalline structures.  Common nonsilicate mineral structures:  cubes, hexagonal prisms, and irregular masses.

 Mineralogist- a person who examines, analyzes, and classifies minerals  Chemical composition and crystalline structure determine a minerals properties  Many of these properties can be used to identify a mineral sample.

Color  Easily observed but unreliable for mineral identification.  Can be affected by impurities or weathering. Streak  Color of a mineral in powdered form  Streak is more reliable than color for the identification of minerals.

Luster  The way a mineral reflects light  Metallic luster- reflects light like polished metals.  Nonmetallic luster- duller appearance  glassy, waxy, pearly, brilliant, and earthy.

 Cleavage- tendency of a mineral to split along specific planes to form smooth, flat surfaces Cleavage and Fracture

Types of Cleavage MuscoviteHalite Feldspar

 Fracture- breaks along curved or irregular surfaces  Uneven or irregular fractures  Splintery or fibrous fractures  Conchoidal fractures Cleavage and Fracture

Hardness  Ability of minerals to resist scratching.  Does NOT mean “resistance to cleavage or fracture.”  Determined by comparing to minerals  Mohs hardness scale the standard scale for the hardness of minerals.  The strength of the bonds between the atoms of a mineral determines its hardness.

Crystal Shape  Certain minerals always have the same general shape because the atoms that form the mineral’s crystals always combine in the same geometric pattern.  The six basic crystal systems:  isometric or cubic, orthorhombic, tetragonal, hexagonal, monoclinic, and triclinic

Density  density the ratio of the mass of a substance to the volume of a substance  The density of a mineral depends on the kinds of atoms in the mineral and on how closely the atoms are packed. density = mass  volume

 The ability to glow under UV light is called fluorescence.  The property of some minerals to glow after the ultraviolet light is turned off is called phosphorescence. Fluorescence and Phosphorescence

Chatoyancy and Asterism  Light is reflected causing a silky appearance that is called chatoyancy  Tiger’s Eye  A similar light reflecting effect called asterism is when a six-sided star appears  Star Sapphire

Double Refraction  Producing a double image of objects viewed through the mineral.

Magnetism  Are attracted to magnets or may be magnetic themselves.  In general, nonsilicate minerals that contain iron are more likely to be magnetic than silicate minerals are.

Radioactivity  The property known as radioactivity results as unstable nuclei decay over time into stable nuclei by releasing particles and energy.  A Geiger counter is used to detect the released particles and, thus, to identify minerals that are radioactive.