Chapter 9: Minerals & Ores 8th Grade Earth Science

9A: Describing Minerals Native Minerals: made of just 1 element Ex: Gold, Silver, Copper Compound Minerals: made of 2+ elements Pure substance Ex: Quartz (Compound of Si & O; SiO2 ) Mixtures: two or more different substances are mixed but are not combined chemically (like cookie dough) If the ratio is different, the compound is something else, NOT Quartz

9B: Identifying Minerals Mineralogist: looks at the physical and chemical properties of small samples of a mineral Different tests are needed to identify a mineral (next series of slides…read on own) Mr. Joan Charles Melgarejo from the University of Barcelona

9B: Identifying Minerals 1) Color: May change in different conditions (exposed to air or water, impurities) Color: Quartz (SiO2)can be green, pink, blue, white, dark grey: Amethyst: quartz with (Manganese) VIOLET COLOR Corundum: colorless, but if contains (Cr), mineral turns red and forms ruby. Sapphire: Quartz that contains little (Fe) and (Ti)

9B: Identifying Minerals 2) Streak: Rub mineral across a streak plate (unglazed porcelain)to test powder color Streak: Some will not produce streak, just scratch the porcelain.

9B: Identifying Minerals 3) Luster: amount and quality of the light it reflects from its surface. Ex: metallic, glassy, pearly, silky, etc. Luster: Copper (metallic), Quartz (glassy), Gypsum (pearly), Diamond (adamantine), Asbestos (silky),

9B: Identifying Minerals 5) Shape: determined by atom shape. 6) Growth: determined by what the mineral is made of Accretion: atoms or ions add one-by-one to the existing crystal structure Pliny the Elder (AD 23-79): one of the first people to describe mineral crystals. Pliny: wrote an encyclopedia on observations of nature called “Natural History”. Died in eruption of Mt. Vesuvius Accretion may happen in water, cooling magma or as hot gases of pure sub. Cool near volcanic vent

9B: Identifying Minerals 7) Cleavage: how minerals split into flat sheets or along certain planes, creating new facets (section) Ex: Mica (perfect), Quartz (none) Fracture: minerals w/o cleavage Ex: uneven (rough surface), hackly (fine points), fibrous, conchoidal (glassy, clam-shell-like chips) 5 ratings for cleavage: perfect, good, fair, poor, none L: Mica R: Quartz

9B: Identifying Minerals 8) Hardness: Mohs scale: 1 (very soft) – 10 (very hard) To figure out a minerals hardness you test it against a known rocks hardness. Talc: 1 Diamond: 10 Friedrich Mohs: 1822, German mineralogist Picture: Talc

9B: Identifying Minerals 9) Specific Gravity: the ratio of a minerals density compared with the density of an equal volume of water. S.G. = density of mineral density of water Ex. Gold has a specific gravity of 19, therefore gold is 19x heavier than water Density = mass/volume

Density = mass/volume

9.7 10) Flame Test: K produces violet flame, Ca produces orange-red flame 11) Acid Test: HCl drops will fizz if mineral contains carbonate, sulfide, or sulfite 12) Magnetism: can be magnetic, nonmagnetic, antimagnetic