Minerals: Building blocks of rocks
Feb 24, 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• unique set of physical properties
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
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
Wavelength of visible light bouncing off a surface
Minerals: Building blocks of rocks
Introduction Properties of minerals
Streak• color of mineral powder• 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• tendency of a mineral to break along planes of
weak bonding when stressed• 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 quartzplagioclase 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