Minerals

1. Minerals mineral = naturally occurring inorganic solid with characteristic chemical composition & crystalline structure Five Characteristic of Minerals 1. occurs naturally 2. inorganic (not made up of living things or remains of living things) 3. solid *4. characteristic chemical composition *5. crystalline pattern = atoms arranged in a pattern repeated over and over * these properties are most important because they distinguish any mineral from all others

2. KINDS OF MINERALS 1. more than 3000 different minerals identified so far (only 30 are common) 2. rock-forming minerals = common minerals that form the rocks of earth’s crust 3. 10 minerals make up 90% of earth’s crust: quartz, orthoclase, plagioclase, muscovite, biotite, calcite, dolomite, halite, gypsum, and ferromagnesian minerals 4. classified into two main groups based on chemical composition

3. Minerals from magma: 1. magma = molten material found beneath Earth’s surface 2. type and amount of elements in magma determine type of minerals formed 3. rate at which magma cools determines size of mineral crystals a. small crystals → cools rapidly b. large crystals → cools slowly

4. Mineral from solution: 1. a given amount of water can only dissolve so much of a solid 2. when water becomes supersaturated (too much) with another substance, mineral crystals may begin to precipitate out of solution 3. can also be formed when water evaporates away leaving mineral behind to form crystals halite

5. Mineral groups: silicates = all minerals containing silicon and oxygen [oxygen most abundant element in crust; silicon second most abundant] 1. usually contains one or more other elements 2. most abundant - 96% of Earth’s crust 3. feldspar and quartz alone make up 50% of earth’s crust

6. 4. types: a. feldspars - most common 1) orthoclase = K 2) plagioclase = Na or Ca or both b. quartz = pure silicon and oxygen c. ferromagnesian minerals - rich in Fe and Mg 1) include hornblende, olivine, muscovite, biotite quartz orthoclase biotite

7. nonsilicates = minerals that do not contain silicon 1. carbonates = has carbonate groups (CO3) & other elements a. primary minerals found in rocks such as limestone, coquina b. some have distinctive colorations [azurite – blue] Ex: calcite, malachite 2. sulfates = has a sulfate group (SO4) and other elements Ex: gypsum malachite Gypsum crystals

8. fluorite 3. halides = other elements with either chlorine, fluorine, iodine, and bromine Ex: halite, fluorite 4. oxides = metal element combined with oxygen Ex: hematite, magnetite 5. sulfides = metal element combined with sulfur Ex: pyrite, chalcopyrite 6. native elements = uncombined elements Ex: copper, sulfur pyrite copper

9. CRYSTALLINE STRUCTURE crystal = natural solid with a definite shape 1. characterized by specific geometric arrangement of atoms 2. position of atoms inside solid produce visible shape 3. X-rays are used to study crystal structure Quartz crystal

10. 4. all silicate mineral structures have same building block a. basic unit is the silica tetrahedron (silicon-oxygen tetrahedron) 1) silicon atom surrounded by 4 oxygen atoms 2) forms pyramid shape with silicon in middle and oxygen at 4 corners b. combines in different arrangements to produce different minerals

11. c. three types of tetrahedra arrangements 1) ionic = tetrahedrons linked only by atoms other than Si and O 2) chains: a) single-chain = tetrahedron bonded to two others by shared oxygen atoms - called pyroxenes b) double-chain = 2 single chains bond to each other - called amphiboles

12. 3) sheets = each tetrahedron shares three oxygen atoms with other tetrahedra d. network silicates = each tetrahedron is bonded to four neighboring tetrahedra mineralogy = study of minerals and their properties mineralogists = scientists who specializes in the study of minerals

13. MINERAL IDENTIFICATION Identification by inspection: 1. color = first and most easily observed property a. only reliable for those that are the same color b. usually isn’t enough to identify a mineral c. impurities can change mineral to various other colors Ex: corundum = colorless corundum + Cr = ruby corundum + Co + Ti = sapphire d. weathered surface may hide color e. need to inspect a freshly exposed surface

14. 2. luster = describes how light is reflected from mineral’s surface a. metallic = reflect light like polished metal Ex: pyrite, galena b. nonmetallic = do not reflect much light 1) usually described by self explanatory words 2) include dull (earthy), pearly, silky, brilliant, glassy (vitreous), transparent, waxy (resinous), adamantine, greasy, and oily 3. texture = how mineral feels to the touch a. used in combination with other tests b. describe as: rough, smooth, ragged, greasy, soapy, or glassy

15. 4. crystal habit = characteristic shape and the manner in which its crystals grow together a. controlled by the arrangement of the atoms b. some can have more than one habit c. crystals need space to grow to develop its shape 1) when growth is obstructed the shape is changed 2) perfectly formed crystals are rare d. crystal faces = flat surface that forms if a crystal grows without obstruction e. six crystal systems: Table 4-1, p.78 1) defined by 3 or 4 imaginary axes that intersect at the center of perfect crystal 2) called crystallographic axes

16. Identification by simple tests: 1. hardness = measures how easily a mineral can be scratched a. controlled by strength of bonds in mineral b. measured by attempting to scratch unknown mineral with object of known hardness 1) if object scratched unknown → unknown is softer than object 2) if object does not scratch unknown → mineral is harder than object

17. c. Moh’s Scale of Hardness = lists hardnesses of ten minerals 1) developed by Friedrich Mohs 2) softest mineral = 1, hardest = 10 3) can use these reference minerals to determine an unknown

18. d. during field work use common objects to test penny = 3.5 common nail = 4.5 fingernail = 2.5 window glass = 5.5 pocketknife = 5.0 steel file = 6.5 e. be sure to check for scratch since powder may rub off from softer minerals Mineral test kit

19. 2. streak = color of a mineral’s powder a. obtained by rubbing mineral across piece of unglazed white porcelain tile = streak plate b. streak will always be same color even though color of mineral may change c. streak color can be different from color of mineral Ex: hematite can be brown, red, or silver → its streak is always reddish-brown

20. d. as a rule 1) metallic minerals generally have a dark streak 2) nonmetallic minerals will have streak that is usually colorless or very light shade of normal color e. test works only for minerals softer than tile f. if mineral has hardness greater than 7, it will not streak

21. 3. way a mineral breaks a. cleavage = tendency to split easily or to separate along flat surfaces Ex: mica, fluorite b. fracture = break with rough or jagged edges or surfaces 1) conchoidal = break into smooth, curved surfaces Ex: quartz, obsidian 2) splintery or fibrous = leaves a jagged surface with sharp edges Ex: copper 3) irregular (uneven) = leaves a rough surface Ex: cinnabar

22. 4. density: helps identify heavier minerals more readily than lighter ones 5. specific gravity = weight of a mineral relative to that of an equal volume of water a. nearly all minerals are denser than water b. typical nonmetallic minerals are slightly less than 3 c. typical metallic minerals are about 5 or greater

23. d. heft = determine density / specific gravity of a mineral by picking up to judge mass 1) must practice with known minerals to develop the feel 2) higher the specific gravity or denser minerals will feel heavier Formula: specific gravity = weight of sample in air weight of equal volume of water = weight of sample in air loss of weight in water

24. Example: A specimen weighs 50 newtons (N) in air and 30 N in water. What is the specific gravity of the specimen? weight in air = 50 N weight loss = 50 N - 30 N = 20 N sp. = 50 N = 2.5 20 N The specimen is 2.5 times as heavy as an equal volume of water.

25. Unique Properties: 1. magnetism = small particles of iron - containing minerals react to magnet Ex: magnetite - most common lodestone - acts as a magnet

26. 2. double refraction = splits light rays into 2 parts a. one ray travels straight through and the other ray is bent b. causes two images to be seen when an object is viewed through transparent specimen Ex: calcite c. refraction = bending of light rays as they pass from one substance to another

27. 3. acid test = specimen reacts producing bubbles a. referred to as effervescence b. use a weak hydrochloric acid solution c. shows substance contains carbonate Ex: calcite

28. 4. fluorescence = ability to glow under ultraviolet light Ex: fluorite 5. phosphorescent = continue to glow after the ultraviolet light is turned off Ex: sphalerite

29. 6. radioactivity = gives off radiation due to unstable nuclei decaying a. can be detected with a Geiger counter b. pitchblende - most common mineral with uranium c. others include carnotite, uraninite, autunite

30. 7. taste = has a characteristic flavor Ex: halite 8. smell = has a characteristic odor Ex: sulfur 9. how sounds when tapped Ex: jade

31. Mineral Uses: ore = mineral that contains a useful substance that can be mined for a profit Ex: hematite = iron; bauxite = aluminum 1. mines are used to remove minerals underground 2. classification of mineral as an ore can change if supply or demand for mineral changes bauxite hematite

32. gemstones = minerals that are prized for their beauty rather than for industrial use 1. have exceptional brilliance, color, durability, and rarity 2. once cut and polished it is called a gem 3. used in jewelry

33. 4. two types: a. precious stones = rarest and most valuable Ex: emeralds, diamonds, rubies, sapphires b. semiprecious stones = more common, so are not as rare and valuable Ex: amethyst, garnet, turquoise, opal opal

34. 5. in its natural form it may look quite different from a gem 6. different from common form of same mineral: a. elements from which it is made Ex: manganese in quartz → purple amethyst b. arrangement of elements → crystal structure 1) allows it to be cut and polished 2) provides information about the internal structure 7. a few gems are not minerals Ex: pearls, amber