geofacts stalactites and other cave formations made from calcium carbonate take thousands of years...
TRANSCRIPT
GeoFacts•Stalactites and other cave formations made from calcium carbonate take thousands of years to form.•One estimate is that a stalactite will grow only 10 cm every 1000 years.
MINERALS
What is a mineral?
Five characteristics of all minerals:naturally occurringinorganic (was never alive)definite crystal structure (atoms arranged in an
orderly pattern)solidspecific chemical composition (made up of different
elements and compounds)Earth’s crust is composed of about 3000
minerals.
Naturally occurring and inorganic…
Minerals are formed from natural processesAny man-made mineral is called synthetic
Minerals are inorganic because they are not alive and never were aliveSalt is a mineral, but sugar is not. Sugar comes
from plants.Coal is not a mineral because it forms over
thousands of years from the buildup of dead/decaying matter.
Definite crystal structure
The atoms in minerals are arranged in regular geometric patterns that are repeated.
This regular formation is called a crystal
Solids with specific compositions
Solids have definite shapes and volumes; liquids and gases do not.
Many atoms have silicon and oxygen in them, but the arrangement and proportion of elements in these minerals are unique.The formula for quartz is SiO2
The formula for pyroxene is MgSiO3
Common elements found in minerals
Eight elements make up 98.5% of the crust’s total mass:
Name Symbol % by Mass
Oxygen O 46.6
Silicon Si 27.7
Aluminum Al 8.1
Iron Fe 5.0
Calcium Ca 3.6
Sodium Na 2.8
Potassium K 2.6
Magnesium Mg 2.1
More than 90% of the minerals in Earth’s crust are compounds containing OXYGEN AND SILICON, the two most abundant elements.
Most minerals are compounds.Quartz is a compound of silicon and oxygenGalena is a compound of lead and sulfur
A few minerals consist of single elements and are called native elements:Examples: silver, copper, sulfur and diamond
Rock-forming minerals
There are 8 minerals that make up most of the rocks of Earth’s crust.
They are primarily composed of the eight most common elements in Earth’s crust.Quartz, feldspar, mica, pyroxeneAmphibole, olivine, garnet, calcite
We’ll talk more about rocks next chapter
Structure of minerals
Identifying minerals
Mineralogy – the study of minerals and their unique properties
Minerals are RARELY identified by one single property
Mineral properties
Color – not the most reliable characteristic; minerals change color with a change in temperature, pressure or metal
Mineral properties
Luster – describes how minerals shine in natural light We classify minerals as having metallic or non-metallic
luster. Not all metallic minerals are metals!! We further classify using words such as vitreous, pearly,
greasy, oily, dull, earthy
Mineral properties
Streak – the color of a mineral’s powder; in many cases the streak will not be the same color as the mineral.The streaks of nonmetallic minerals are usually colorless
or white
Mineral properties
Hardness – resistance to being scratchedDiamond is the hardest of all minerals. Talc is the softest of all minerals.
The minerals in the table on the next slide were selected because they are easily recognized and are readily found in nature (except for diamond).
Mohs Scale of HardnessFriedrich Mohs
devised a numeric scale that is used to express the hardness of minerals.
You can determine the approximate hardness of any common mineral by using other common objects
Mineral Hardness Comparison
Talc 1
Gypsum 2 Fingernail = 2.5
Calcite 3 Copper penny = 3.5
Fluorite 4 Iron nail = 4.5
Apatite 5 Glass = 5.5
Feldspar 6 Steel file = 6.5
Quartz 7 Streak plate = 7
Topaz 8
Corundum 9
Diamond 10
Mineral properties
Specific gravity – ratio of a mineral’s mass to the mass of an equal volume of water
It tells you how many more times denser the mineral is than water.
Mineral properties
Texture – the way a mineral feels
This property is very subjective; a mineral may feel different to two people working together
Special properties
HCl chemical test: look for bubbles to formDouble refraction: shows a double imageFluorescence: the ability to glow under UV lightPhosphorescence: the ability to glow in the darkMagnetism: attraction to magnets
Silica Tetrahedron
More than 90% of the minerals in Earth’s crust are silicates.
Silicon and oxygen bond in a way that forms a tetrahedron
Mineral groups
Silicates – quartz and feldspar are the most common minerals found in this groupUses: gems, watches, potting soil additive
Carbonates – calcite and dolomite are the most common mineralsUses: cement for construction, paper, medicines
Mineral groups
Oxide – mineral that has oxygen combined with a metal element; hematite and magnetite are common mineralsUses: abrasives, plumbing fixtures, auto parts
Sulfide – mineral that has sulfur combined with a metal element; pyrite (fool’s gold) and galena are common mineralsUses: jewelry, ores for manufacturing
Mining for minerals
Ores and mines
Ore – minerals that contain useful substances that can be mined for a profit
The classification of a mineral as an ore can also change if the supply of or demand for that mineral changes.
Ores that are located deep within Earth’s crust are removed by mining
Consequence of mining???
Gems
Some minerals are rarer than others and are therefore classified as expensive gems.
Gems – valuable minerals that are prized for their rarity and beauty
Rubies and emeralds are more expensive than diamonds.