Minerals: Building blocks of rocks
Jan 17, 2016
Minerals:
Building blocks of rocks
Minerals: Building blocks of rocks
Introduction
• What are minerals and how are they different from rocks?
• What are some of the physical and chemical properties of minerals?
• What is the most abundant mineral group? What do all minerals in this group have in common?
• What are some important nonsilicate minerals?
• When is the term ore used with reference to a mineral?
Minerals: Building blocks of rocks
Introduction Definitions
Minerals versus rocks
• rock – an aggregate of minerals
• aggregate – minerals occur together as a mixture
• each mineral retains its distinctive properties
• mineral – a naturally occurring inorganic solid that possesses a definite chemical structure, which gives it a unique set of physical properties
Minerals: Building blocks of rocks
Introduction
Minerals exhibit the following characteristics:
• naturally occuring
• inorganic
• solid
• definite chemical structure
Definitions
Minerals: Building blocks of rocks
Introduction Properties of minerals
Major properties of minerals:
• crystal form
• luster
• color
• streak
• hardness
• cleavage
• fracture
• specific gravity
Minerals: Building blocks of rocks
Introduction Properties of minerals
Crystal form – external arrangement of the orderly internal arrangement of atoms
Minerals: Building blocks of rocks
A supersaturated solution readily forms crystals
Crystallization occurs when the KE of individual molecules decreases.
Introduction Properties of minerals
Crystal form – clearly evident only when the mineral forms without space restrictions
Crystals form as they overcome solvation forces
Most minerals form under intense competition for space
Minerals: Building blocks of rocks
Introduction Properties of minerals
Luster – appearance or quality of light reflected from the surface
Minerals: Building blocks of rocks
Introduction Properties of minerals
Luster
• metallic luster
• submetallic luster
• nonmetallic luster
• vitreous
• pearly
• silky
• resinous
• earthy
Minerals: Building blocks of rocks
Introduction Properties of minerals
Color – very unreliable diagnostic property due to impurities
Minerals: Building blocks of rocks
Introduction Properties of minerals
Streak
• color of a mineral in its powdered form
• use a streak plate
• more reliable than color
• metallic (dense, dark streak) vs. nonmetallic
Minerals: Building blocks of rocks
Introduction Properties of minerals
Minerals: Building blocks of rocks
Introduction Properties of minerals
Hardness
• resistance of a mineral to abrasion or scratching
• use the Mohs scale
Minerals: Building blocks of rocks
Introduction Properties of minerals
Cleavage
• a mineral will break along weak bonds when stressed
• tendency of a mineral to break along planes of weak bonding
• cleavage is described by the number of planes formed and the angles in which these planes meet
• not all minerals have definite planes of cleavage
Minerals: Building blocks of rocks
Introduction Properties of minerals
Some examples of cleavage
Minerals: Building blocks of rocks
Introduction Properties of minerals
Fracture
• minerals that do not exhibit cleavage tend to fracture when broken
• conchoidal fracture – produces smooth curved surfaces
• other types of fracture (splinters or fibers)
• most minerals fracture irregularly
Minerals: Building blocks of rocks
Introduction Properties of minerals
Some examples of fracture
Fibrous fracture – note formation of parallel fibers Conchoidal fracture
– note smooth curved surfaces
Minerals: Building blocks of rocks
Introduction Properties of minerals
Specific gravity - compares the weight of a mineral to the weight of an equivalent volume of water
Minerals: Building blocks of rocks
Introduction Mineral groups
Mineral groups
Silicates
• most common
• made of oxygen and silicon
• silicon-oxygen tetrahedron is the fundamental building block
Minerals: Building blocks of rocks
Introduction Mineral groups
Variants of the silicate structure
• addition of metals to stabilize structure (Fe, Mg, K, Na, Al, and Ca)
• sharing of oxygen atoms results to a variety of configurations
• single chains
• double chains
• sheets
Minerals: Building blocks of rocks
Introduction Mineral groups
Minerals: Building blocks of rocks
Introduction Mineral groups
Variants of the silicate structure
• the ratio of oxygen to silicon atoms varies among the different silicate structures
• high or low silicon content based on this ratio
• important in the formation of igneous rocks
• families of minerals
• same structure but with varying amounts of metals
• olivine, (Mg,Fe)2SiO4
Minerals: Building blocks of rocks
Introduction Mineral groups
Dark silicate minerals
• ferromagnesian silicates
• contains iron and/or magnesium
• dark color and greater specific gravity
Minerals: Building blocks of rocks
Introduction Mineral groups
olivine
hornblende biotite
Minerals: Building blocks of rocks
Introduction Mineral groups
Light silicate minerals
• nonferromagnesian silicates
• contains Al, K, Ca, and/or Na
• light color and smaller specific gravity
Minerals: Building blocks of rocks
Introduction Mineral groups
Light silicate minerals
• feldspars – most common light silicates (most common mineral on Earth)
• orthoclase feldspar – has K ions
• plagioclase feldspar – has Na and Ca
• light color and smaller specific gravity
• quartz – consists entirely of silicon and oxygen
Minerals: Building blocks of rocks
Introduction Mineral groups
rose quartz
plagioclase feldspar
orthoclase feldspar
Minerals: Building blocks of rocks
Introduction Mineral groups
Nonsilicate minerals
• carbonate minerals (limestone)
• halite (table salt)
• gypsum (used in plaster, building materials)
• metal ores (Fe, Zn, Pb)
• native elements – free occurring, not in compounds (Au, Ag, C)
Minerals: Building blocks of rocks
Introduction Mineral groups
limestone
Minerals: Building blocks of rocks
Introduction Mineral groups
pink halite
gypsum
Minerals: Building blocks of rocks
Introduction Mineral groups
malachite
Minerals: Building blocks of rocks
Introduction Mineral groups
Minerals: Building blocks of rocks
Introduction Mineral groups