ATOMS TO MINERALSGeoFactsPart Two•Stalactites and other cave formations made fromcalcium carbonate take thousands of years to form.•One estimate is that a stalactite will grow only 10cm every 1000 years.
What is a mineral?• Five characteristics of all minerals:• naturally occurring• inorganic (was never alive)• definite crystal structure (atoms arranged in anorderly pattern)• solid• specific chemical composition (made up of differentelements and compounds)• Earth’s crust is composed of about 4000minerals.
Naturally occurring and inorganic…• Minerals are formed from natural processes• Any man-made mineral is called synthetic• Minerals are inorganic because they are not aliveand never were alive• Salt is a mineral, but sugar is not. Sugar comesfrom plants.• Coal is not a mineral because it forms overthousands of years from the buildup ofdead/decaying matter.
Definite crystal structure• The atoms in minerals are arranged in regulargeometric patterns that are repeated.• This regular formation is called a crystal
Solids with specific compositions• Solids have definite shapes and volumes; liquidsand gases do not.• Many atoms have silicon and oxygen in them,but the arrangement and proportion of elementsin these minerals are unique.• The formula for quartz is SiO 2• The formula for pyroxene is MgSiO 3
Common elements found in minerals• Eight elements make up 98.5% of the crust’stotal mass:Name Symbol % by MassOxygen O 46.6Silicon Si 27.7Aluminum Al 8.1Iron Fe 5.0Calcium Ca 3.6Sodium Na 2.8Potassium K 2.6Magnesium Mg 2.1
• More than 90% of the minerals in Earth’s crustare compounds containing OXYGEN ANDSILICON, the two most abundant elements.• Most minerals are compounds.• Quartz is a compound of silicon and oxygen• Galena is a compound of lead and sulfur• A few minerals consist of single elements andare called native elements:• Examples: silver, copper, sulfur and diamond
Rock-forming minerals• There are 8 minerals that make up most of therocks of Earth’s crust.• They are primarily composed of the eight mostcommon elements in Earth’s crust.• Quartz, feldspar, mica, pyroxene• Amphibole, olivine, garnet, calcite• We’ll talk more about rocks next chapter
Structure of minerals
Silica Tetrahedron• More than 90% of theminerals in Earth’scrust are silicates.• Silicon and oxygenbond in a way thatforms a tetrahedron
Identifying minerals• Mineralogy – the study of minerals and theirunique properties• Minerals are RARELY identified by one singleproperty
Mineral propertiesColor – not the most reliable characteristic; mineralschange color with a change in temperature,pressure or metal
Mineral propertiesLuster – describes how minerals shine in natural light• We classify minerals as having metallic or non-metallicluster. Not all metallic minerals are metals!!• We further classify using words such as vitreous, pearly,greasy, oily, dull, earthy
Mineral propertiesStreak – the color of a mineral’s powder; in many casesthe streak will not be the same color as the mineral.• The streaks of nonmetallic minerals are usually colorlessor white
Mineral propertiesHardness – 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 wereselected because they are easily recognized and arereadily found in nature (except for diamond).
Mohs Scale of Hardness• Friedrich Mohsdevised a numericscale that is used toexpress thehardness ofminerals.• You can determinethe approximatehardness of anycommon mineral byusing other commonobjectsMineral Hardness ComparisonTalc 1Gypsum 2 Fingernail = 2.5Calcite 3 Copper penny = 3.5Fluorite 4 Iron nail = 4.5Apatite 5 Glass = 5.5Feldspar 6 Steel file = 6.5Quartz 7 Streak plate = 7Topaz 8Corundum 9Diamond 10
Mineral propertiesSpecific gravity – ratio ofa mineral’s mass to themass of an equalvolume of waterIt tells you how manymore times denser themineral is than water.
Mineral propertiesTexture – the way a mineral feelsThis property is very subjective; a mineral may feeldifferent to two people working together
Special properties• HCl chemical test: look for bubbles to form• Double refraction: shows a double image• Fluorescence: the ability to glow under UV light• Phosphorescence: the ability to glow in the dark• Magnetism: attraction to magnets
Mineral groups• Silicates – quartz and feldspar are the mostcommon minerals found in this group• Uses: gems, watches, potting soil additive• Carbonates – calcite and dolomite are the mostcommon minerals• Uses: cement for construction, paper, medicines
Mineral groups• Oxide – mineral that has oxygen combined witha metal element; hematite and magnetite arecommon minerals• Uses: abrasives, plumbing fixtures, auto parts• Sulfide – mineral that has sulfur combined with ametal element; pyrite (fool’s gold) and galena arecommon minerals• Uses: jewelry, ores for manufacturing
Mining for minerals
Ores and mines• Ore – minerals that contain useful substancesthat can be mined for a profit• The classification of a mineral as an ore can alsochange if the supply of or demand for thatmineral changes.• Ores that are located deep within Earth’s crustare removed by mining• Consequence of mining???
Gems• Some minerals are rarer than others and aretherefore classified as expensive gems.• Gems – valuable minerals that are prized fortheir rarity and beauty• Rubies and emeralds are more expensive thandiamonds.