What is a mineral?
A mineral is a naturally occurring inorganic solid with a definite chemical composition and orderly atomic arrangement.
Quartz, Halite, Mica, Gold, and Diamond
Water? Glass? Pearl?
Most minerals are compounds!
Eight elements make up 98.5 percent of the total mass of Earth’s crust.
Oxygen (46.6 % by Mass) and Silicon (27.7 % by Mass)
Aluminum, Iron, Calcium, Sodium, Potassium, and Magnesium.
Most elements occur combined with other elements.
How does a compound form?
Atoms are electrically neutral!
If an atom loses one or more electrons, it becomes positively charged.
An atom that is positively charged is an cation.
This ion is attracted to a negatively charged atom. (that has extra electrons - anion)
This attraction is a IONIC BOND! It is a GIVING AND TAKING of electrons!
NaCl (Sodium Chloride)
Ionic Bonding in Minerals
Ionic bonds form between METALS that lose electrons to form positive ions and NONMETALS that gain electrons to form negative ions.
Covalent Bonding in Minerals
The kind of attachment were electrons in a molecule are SHARED are called covalent bonds!!!
NON-METAL + NON-METAL
Example
Quartz = silicon + oxygen (covalently bonded)
How does a mineral form?
Minerals can form several ways.
Magma cooling -volcanoes
Water containing dissolved ions evaporates!
When salt water evaporates - Halite!
THE RATE AT WHICH MAGMA COOLS DETERMINES THE SIZE OF THE MINERAL GRAINS THAT FORM!
Crystals
Crystal - a regular geometric solid with smooth surfaces called crystal faces.
The orderly arrangement of the ions determines the shape of the crystal.
Halite - faces meet at right angles.
Quartz - faces meet at an angle of 120 degrees.
The 6 different Crystal Shapes!
Cubic System - Three axes of equal length that intersect at 90 degree angles.
Halite
Orthorhombic System - Three different axes of different length that intersect at 90 degree angles.
Sulfur and Topaz
Tetragonal System - Three axes that intersect at 90 degree angles.
Wulfenite and Chalcopyrite
Triclinic System - Three axes of unequal length that intersect at oblique angles.
Turquoise and Kyanite
Hexagonal System - Three horizontal axes that are the same length and intersect at 60 degree angles. A vertical axis that is longer than the horizontal axes.
Quartz and Graphite
Monoclinic System - Three unequal axes, two intersect at 90 degrees, the third is oblique to the other two.
Gypsum and Borax
Minerals have a crystalline structure
Silicate minerals make up over 90 percent of Earth’s Crust.
The crystal shape, hardness, cleavage, and density of a mineral are determined by the internal arrangement of its atoms or ions.
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