Minerals

1. Minerals Chapter 5

2. What is a mineral? • Minerals are the building blocks of rocks.. All of them are solid. • They occur naturally and have a definite chemical composition • The atoms are arranged in an orderly fashion (crystal) • Inorganic (never alive)

3. How many minerals are there? • Well, there about 4000 known but there are a whole lot more I am sure to be found. • Minerals can be elements like lead or compounds like feldspar • Most are compounds

4. Elements of earth—native elements • Even though there are 92 elements that are naturally found, only 8 elements make up more than 98% of the earth’s crust. • 46.6% Oxygen (O)27.7% Silica (Si)8.1% Aluminum (Al)5.0% Iron (Fe)3.6% Calcium (Ca)2.8% Sodium (Na)2.6% Potassium (K)2.1% Magnesium (Mg)

5. Compounds of the earth • Most minerals are compounds. • Quartz is the most common chemical compound in the earth's crust. We know it better as common beach sand. Si02

6. Mineral formation • Process of crystallization • Growth of a solid from a gas or liquid whose constituent atoms come together in the proper chemical proportions and crystalline arrangement

7. When do minerals form? • Cooling of magma (quartz) • Precipitation from saturated solution (halite) • Atoms and ions become mobile an rearrange themselves at high temperatures (pyroxene)

8. The earth, the other inner planets and the moon are made of ROCKS.Rocks in turn, are made of MINERALS

9. Minerals of one type of atom - native elements (Au - gold, Ag - silver, Cu - copper, among others). How are minerals formed?

10. Minerals with cations combined with the large, negative ions (anions): oxygen (O - oxides), sulfur (S - sulfides), halogens (Cl, F or Br - halides) .

11. and anions groups made of oxygen combined with cations of valency +3 or greater (see periodic table - non-metals of groups 13-17): silicates (SiO4), carbonates (CO3) and sulfates (SO4).

12. Only a dozen minerals account for most of the world's rocks. • Plagioclase feldsparNaAlSi3O8 to CaAl2Si2O8 • Potassium feldsparKAlSi3O8 • QuartzSiO2 • Pyroxene(Mg,Fe)2Si2O6 and Ca(Mg,Fe)Si2O6 (augite)

13. BiotiteK(Fe,Mg)3AlSi3O10(OH)2 Hornblende(Ca,Na)2–3(Mg,Fe,Al)5[(Si,Al)8O22](OH)2 Olivine(Fe,Mg)2SiO4 MagnetiteFe3O4 Garnet(Ca,Mg,Fe2+)3(Al,Fe3+)2Si3O12 CalciteCaCO3DolomiteCaMg(CO3)2

14. Physical properties of minerals • Classifying minerals can range from simple to very difficult. A mineral can be identified by several physical properties. • Sometimes minerals can only be classified by chemical or X-ray diffraction analysis; these methods, however, can be costly, time-consuming, and even risk damaging the sample.

15. Crystal structure • See page 99 • It is the arrangement of atoms that determines the shape…(just to repeat) • Each mineral has its own unique form • The angle at which crystal faces meet is unique and can be used to identify the mineral

16. Crystal structure • Not all minerals form crystal faces….if the space is limited when forming there is no room for a “face” to form.

17. Silicates • Minerals that contain oxygen and silicon • May include other metallic elements Staurolite, Fe2Al9O • A few silicates do not have metal included----quartz • 90% of all minerals are silicates

18. Silica tetrahedron • The basic building blocks of all silicates is the silica tetrahedron

19. Crystal structure and habit: A mineral may show good crystal habit or form, or it may be massive, granular or compact with only microscopically visible crystals. Physical identification

20. Hardness: • Mohs scale is relative and goes from 1 to 10. Minerals with a given Mohs hardness can scratch the surface of any mineral that has a lower hardness than itself. The minerals that define the scale are given below: • 1- talc 2- gypsum 3- calcite 4- fluorite 5- apatite 6- orthoclasefeldspar 7- quartz 8- topaz or beryl 9- corundum 10- diamond

21. Mineral Properties • luster  hardness  streak  cleavage  fusibility  specificgravity  habit  tenacity  color  luminescence  radioactivity magnetism

22. Luster • A mineral’s luster is the overall sheen of its surface – it may have the sheen of polished metal, or that of an unpolished metal that is pitted by weathering – or it may have the sheen of glass, or look dull or earthy, etc

23. Luster cont’d • Adamantine, having the hard, sparkly look of a diamond • Glassy/Vitreous, having the look of glass; • Resinous, having the look of amber – not quite glassy; • Pearly, having the iridescent look of mother-of-pearl (though usually just barely); • Greasy/Oily, having the look of an oil-coated substance; • Silky, having the look of silk, fine parallel fibers of mineral – such as chrysotile "asbestos;" • Dull, having a plain looking surface that is not submetallic; • Earthy, having the look of soil or clay

24. color • a double-edged sword in mineral identification:  There are many minerals which have distinctive colors; but there are also many which come in a variety of hues.  And the same color can be seen in several different species

25. Color cont’d • Opalescence, an opal-like play of light, reflections off the mineral producing flashes of color that may appear somewhat like a patch-work of different "grains" of color that aren’t really there:  Move the sample minutely and the color disappears from that spot. 

26. Color cont’d • Iridescence is similar to opalescence except that it is usually associated with metallic minerals and surface reflections rather than glassy minerals and sub-surface reflections:  An exception is the type of iridescence known as labradoresence

27. Color cont’d • Luminescence is the emission of light by a mineral other than the reflected light of the sun or a lamp – the mineral "glows" due to some other reason.

28. Chatoyancy • Chatoyancy is the play of light off closely packed parallel fibers or parallel inclusions in cavities.  The light reflects along lines – which may be straight or curved – giving the mineral a somewhat silky appearance.  This characteristic is seen in such minerals as "satin spar" gypsum, "tiger’s eye" (fibrous crocidolite replaced by quartz), and chrysoberyl

29. Fusibility • The measure of how much heat it takes to melt a mineral into a globule, or at least to melt the sharp edge of a sharp splinter and make it round over.

30. specificgravity Density and Specific Gravity are not properties easily determined, requiring special equipment. "heft" can come in handy:  The denser a mineral is, the heavier it is per given volume.  A 1 inch cube of galena is noticeable heavier in the hand than a 1 inch cube of pyrite.    With a little practice a collector can become good judging the relative weight of minerals and using that to help establish a sample’s identity.

31. habit • Habit is the general appearance a mineral tends to have – whether it is found as blocky crystals, long slender ones, or aggregates of some type, etc.  • Distinct crystals may be described by the following……..see website

32. Tenacity • refers to a mineral’s resistance to breaking, bending, or otherwise being deformed.  A mineral may be: • brittle, malleable, sectile, flexible, elastic,

33. Streak • Streak is simply the color of a mineral powder.  Many minerals have a different color when powdered than they do in crystal or massive forms. The color may be entirely different, or it may be a different shade.

34. specificgravity Density and Specific Gravity are not properties easily determined, requiring special equipment. "heft" can come in handy:  The denser a mineral is, the heavier it is per given volume.  A 1 inch cube of galena is noticeable heavier in the hand than a 1 inch cube of pyrite.    With a little practice a collector can become good judging the relative weight of minerals and using that to help establish a sample’s identity.

35. Cleavage • Cleavage refers to the way some minerals break along certain lines of weakness in their structure. 

36. Radioactivity • is another property that, while not too common, is found in some minerals and can be useful in identification.  Collectors who have a Geiger counter may find it useful at certain localities, particularly pegmatite – where many of the more common radioactive minerals are found.

37. Fracture • Minerals break in directions other than along cleavage surfaces • Conchoidal—shell like--smooth • Splintery—leave jagged edge • Uneven or irregular—rough surface

38. Chemical tests • Reaction with acid—calcite (CaCO3) fizzes and releases carbon dioxide gas

39. Special properties • Double refraction—causes a single object to appear as two

40. Simple kit • A piece of plain white paper (a blank specimen label works great.) • Your fingernails (preferable still attached to your fingers!) • A copper penny (or small –½ inch – piece of copper or short piece of heavy copper wire.) • A small piece of fluorite (a broken cleavage piece is fine.) • A pocket knife (NOT a Swiss Army knife – the steel in those is harder than in most cheap pocket knives, which can throw hardness tests off.) • A small section of a steel file (a 2 or 3 inch tip from a triangular file for sharpening chain saws works fine.) • A piece of a quartz crystal (with at least one good face and a sharp point - a broken section

41. Simple kit cont’d • usually has a sharp point on it somewhere, it doesn’t have to be a crystal termination.) • A small piece of a beryl or topaz crystal (with at least one good face and a sharp point or edge.) • A small piece of a corundum crystal (with at least one good face and sharp point or edge.) • A "streak plate" (unglazed porcelain tile – a 2 inch square is plenty.) • A short candle stub and matches (in waterproof container) or a cigarette lighter. • A small pair of tweezers. • A small magnet (a refrigerator magnet is fine, but should be a fairly strong one.) • A 10x hand lens/jeweler’s loupe. • Blank specimen labels. • Pens or pencils.

42. Mineral groups • Major silicates comprise 90% of earth minerals • Classified by ways the tetrahedral linked together see page 101

43. Quartz • Entirely tightly bound silica tetrahedral • Glass or greasy luster • Pure quartz-colorless or white • Colored quartz—amethyst, rose, smoky,