Learning Target = Matter & Minerals

Mineral Characteristics Definition = naturally occurring, inorganic solid with an orderly crystalline structure and a definite chemical composition To be considered a mineral, must have the following characteristics: Naturally occurring Solid substance Orderly crystalline structure Definite chemical composition Generally considered inorganic

Mineral Characteristics Naturally occurring – formed by geologic processes Solid substance – solids within temp ranges that are normal for Earth’s surface Crystalline structure – atoms or ions arranged in orderly & repetitive manner Definite chemical composition – most minerals are chemical compounds Generally considered inorganic – minerals generally do not come from a living source

How Minerals Form 4 major processes by which minerals form: Crystallization from Magma Precipitation Pressure & Temperature Hydrothermal Solutions

How Minerals Form Crystallization from Magma As magma (molten rock) cools, elements combine and crystallize 1st – compounds rich in Fe, Ca, Mg 2nd – Na, K, Al Muscovite Feldspar Horneblende Quartz

How Minerals Form Precipitation Water contains dissolved substances Minerals form due to: Evaporation Temperature change Minerals are left behind

How Minerals Form Pressure & Temperature Increase in pressure causes a mineral to recrystallize Form more compact minerals Temperature change can cause instability and new minerals form that are stable at new temperature Ex: Talc & Muscovite

How Minerals Form Hydrothermal Solutions Hot mixture of water & dissolved substances Temps = 100°C & 300°C Chemical reactions form new minerals Solutions cool & minerals form as well Ex: Quartz, pyrite, sulfur minerals

Mineral Groups Over 3,800 identified minerals Groups are based on composition Silicates Carbonates Oxides Sulfates & sulfides Halides Native elements

Silicates Silicon & oxygen = most abundant elements in Earth’s crust Si and O combine & form the silicon-oxygen tetrahedron (SiO4) Usually contain other elements Si-O tetrahedra join in different ways & bonds are strong

Olivine Augite Hornblende Quartz Mica

Silicates Crystallization from magma Cooling occurs at or near Earth’s surface (temp and pressure low) Also form at great depths (T & P ↑) Silicate formation dependent on: Place of formation Chemical composition of magma

Carbonates 2nd most common group Contain C, O & another metallic element Calcite (CaCO3) is most common Ex: Dolomite, limestone (rock), marble (rock)

Oxides Contain O + 1 or more elements (usually metals) Form by: Magma cooling Changes in T and P Exposed to water or moisture in air Ex: Rutile (TiO2), Corndum (Al2O3), Hematite (Fe2O3)

Sulfates & Sulfides Contain Sulfur Form when mineral-rich waters evaporate Form from thermal solutions Ex: Gypsum, Galena, Pyrite

Halides Contain a halogen ion plus 1 or more elements Ex: Halite (NaCl) & Fluorite (CaF2)

Native Elements Contains one element Ex: Gold (Au), Silver (Ag), Copper (Cu), Sulfur (S), Carbon (C) Native forms of carbon are graphite & diamond Some form from hydrothermal solutions

Properties of Minerals Color Streak Luster Crystal form Hardness Cleavage Fracture Density Distinctive properties

Properties of Minerals Color Can be unique to some minerals Not useful in identification Small amounts of different elements can give the same mineral different colors Ex: Sapphires

Properties of Minerals Streak Color of a mineral in its powdered form Rub mineral across a streak plate Mineral color may vary but streak does not Difference between minerals with metallic & nonmetallic lusters

Properties of Minerals Luster How light is reflected from the surface of a mineral Metallic luster – appearance of metal Nonmetallic luster – use different adjectives Glassy or vitreous Pearly Silky Earthy Brilliant

Properties of Minerals Crystal form Visible expression of a mineral’s internal arrangement of atoms When a mineral forms slowly with plenty of space, develop into a crystal with well-formed sides Most of the time, minerals compete for space so minerals do not show their crystal form

Properties of Minerals Hardness Measure of the resistance of a mineral to being scratched Determined by rubbing one mineral against another of known hardness Mohs scale consists of 10 minerals arranged from 10 (hardest) to 1 (softest)

Properties of Minerals Cleavage Tendency of a mineral to break along flat, even surfaces

Properties of Minerals Fracture Uneven breakage of a mineral Minerals that do not show cleavage when broken are said to fracture

Properties of Minerals Density Property of all matter that is the ratio of an object’s mass to its volume Unit = grams per cubic centimeter (g/cm3) Many common minerals have densities between 2 & 5 g/cm3

Properties of Minerals Distinctive Properties of Minerals Some minerals can be recognized by other distinctive properties Feel (Talc = soapy, graphite = greasy) Easily shaped (Gold, silver, copper) Magnetic Double refraction (appearance doubles) Smell (sulfur minerals = rotten eggs) Reacts with hydrochloric acid