Geology 50 Laboratory Manual

Minerals

The Earth is the source of all things that we do; everything we use in day to day society come from naturally-occurring chemical compounds called minerals. To be sure several of the giant chemical companies give us better living through rearranging the chemicals, but these new products are made from the starting chemicals of the Earth, i.e. minerals. In the exercise that follows you will learn about some 20 minerals that are important not only to understanding geology, but also important to your everyday life.

We have just introduced above the beginning of a formal definition of a mineral. You may have already heard in lecture or in your text that a mineral is

1.) naturally occurring 2.) solid 3.) inorganic (not made by biological synthesis, i.e. not organic) 4.) a definite chemical composition (a unique formula can be written) 5.) crystalline (an orderly internal atomic arrangement, not amorphous like glass).

The 20 minerals that you will study are but a small portion of the more than 2000 known minerals. Such a huge study might still be fun if all the samples were at least gemstones! But how do even the experts tell so many minerals apart? Clearly the chemistry itself, from the third item of the definition above, would classify and characterize one mineral from another. But this is geology lab, not a chemistry lab, so what other criteria can be used to identify and classify the 20 assigned minerals? How could you use the fourth item in the definition above? Without some X-ray equipment to examine the atomic internal structure, you could not. And again this is not a physics lab, but a geology lab.

So clearly the formal definition of a mineral will not help a non-scientist to classify these materials. Since this lab course is mostly populated by people like yourself, i.e.,non-science majors, how can we expect you to succeed in learning the differences in these 20 minerals? Again from lecture or your text, you may have already found out that there are useful characteristics such as color, luster, fracture, cleavage. And a little bit more abstract are properties like

19 hardness, and density (specific gravity or how heavy does the sample feel in your hand). These properties are quite useful to differentiate the minerals. Hence this lab is really about those properties and how to use them to classify and identify minerals.

The most reliable property as a first screening is hardness. The Moh’s hardness scale was built up by an Austrian mineralogist (in 1822) who wanted to pick minerals as common as possible and arrange them into an increasing hardness scale from 1(softest) to 10(hardest):

HARDNESS MINERAL COMPRABLE USE IN HARDNESS EVERYDAY LIFE 1 talc Very soft Talcum powder 2 gypsum fingernail Plaster of Paris, wall board 3 calcite > copper coin Cement, agricultural lime 4 Fluorite Fluoride for toothpaste 5 apatite Window glass Tooth enamel (calcite+apatite 6 orthoclase Iron nail “granite”-glazed cooking pans 7 quartz >window glass Transponder in telephones 8 topaz >steel knife/pin Blue topaz gemstone 9 corundum White sandpaper 10 diamond Synthetic Gem and tooling ceramics

Later work showed that a good diamond has a maximum hardness of as much as 32 on this scale. Since Moh’s day, several synthetic ceramics like boron nitride (H=28) or zirconium oxide (H=9.5) have been prepared from their appropriate minerals and found to have hardnesses that fall between corundum and diamond.

20 Consider the following questions from everyday life:

To scratch glass what is the best choice of minerals?

Does using steel wool on the granite glaze to remove a bath tub ring make sense? Why?

Would a ceramic knife made from zirconium oxide stay sharp longer than steel ? Why?

Here in the lab, your Teaching Assistant will circulate some minerals from a hardness kit and suggest some hands on tests for you to try with the minerals in your lab desk drawer.

Learn that you can be fooled in making your hardness tests…be sure that the apparent scratch is really a groove and not just a line of powder left by a softer mineral on the harder mineral. For example, chalk (fossil skeleton of diatom) on the blackboard means that the chalk is the softer material as the slate blackboard will wipe clean and show no scar or groove to mar its surface.

Thus with the supplied iron nail, you can divide all 20 minerals into two piles:

Softer than the iron nail and harder.

Now split each hardness pile into three piles for light-colored or dark-colored or metallic-looking, for a total of six separate piles.

Schematically this is as follows:

H<6 Light Dark Metallic All 20 samples

Light H>6 Dark Metallic 21 If we add just one more characteristic, we will have a very reliable way to work towards a mineral identification by ‘pigeon-holing’ from left to right in the above type of network. We could use specific gravity, or the color of a streak of the powder made by rubbing the mineral on a streak plate (unglazed porcelain tile), or we could use the property of cleavage/fracture. With a bit of practice, the cleavage/fracture is easiest to learn and the others can be held in reserve to ‘clinch’ an ID made by using cleavage/fracture.

Minerals must have, by definition, an orderly internal atomic arrangement (item #4 of our definition). Thus, it comes as no surprise that when they are broken, this internal arrangement usually controls the appearance of the broken surface. We are all used to seeing a random wavy-fracture (called conchoidal) on the edge of a broken glass bottle or the ‘spider-web’ in the plane of the broken window glass. This conchoidal fracture results because the glass is amorphous with not much internal order. The spider-web cracking is a breakage pattern in plate glass that results from a point impact and as the shock waves radiate out from the impact point, the shock wave bounces back and forth between the two planes of the glass and dissipates the energy by breaking the amorphous glass in ever expanding concentric rings until the shock energy is too weak to break the glass anymore. But the orbs of the ‘web’ are random because there is no orderly internal atomic arrangement in the glass. However, when minerals break the exact atoms and their sizes and arrangements in their crystalline structure control the type of cleavage-breakage that does occur. Thus without being a chemist or a physicist, one can use the cleavage shape as one discriminator to identify different minerals. The figure at the end of this lab shows that one way to describe cleavage is by the number of planes and the angles these planes make to each other.

In the figure each type of fracture or cleavage has planes drawn to help visualize in 3 dimensions how the trace of the cleavage direction extends. The diagrams show how the number of planes relate to a solid polygonal shape. And the ‘lump’ diagrams show how these planes may appear in typical hand samples of minerals. Can you find samples that show each type of fracture or cleavage?

As you feel confident of cleavage/fracture further subdivide the identification process as shown in Tables 1 and 2. Note that we will skip cleavage/fracture for the metallic mineral classification where we have only one mineral for each hardness.

22 LIST OF MINERALS (alphabetic)

Name Chemistry in words Chemistry in symbols

Amphibole Iron-magnesium hydroxy alumino-silicate (Hornblende) Apatite Calcium hydroxy phosphate Ca5(PO4)3(OH) Biotite Potassium,iron-magnesium hydroxy alumino-silicate K(Mg,Fe)3AlSi3O10(OH)2 Calcite Calcium carbonate CaCO3 Corundum Aluminum oxide Al2O3 Dolomite Calcium-magnesium carbonate CaMg(CO3)2 Fluorite Calcium fluoride CaF2 Galena Lead sulfide PbS Garnet Iron-magnesium alumino-silicate (Fe,Mg)3Al2(SiO4)3 Gypsum Calcium sulfate hydrate CaSO4.2H2O Halite Sodium chloride NaCl Hematite Iron oxide Fe2O3 Magnetite Magnetic iron oxide Fe3O4 Muscovite Potassium hydroxy alumino-silicate KAl3Si3O10(OH)2 Olivine Iron-magnesium silicate (Fe,Mg )2SiO4 Orthoclase (feldspar) Potassium alumino-silicate KAlSi3O8 Quartz Silicon dioxide SiO2 Plagioclase (feldspar) Sodium-calcium alumino-silicate (Na,Ca)Al2Si2O8 Pyroxene Calcium, iron, magnesium silicate (Ca,Mg,Fe)Si2O6 (Augite) Talc Hydrous magnesium silicate Mg3Si4O10(OH)2

LIST OF SOME USES OF THESE 20 MINERALS

SILICATES

Orthoclase- is melted to make glazed items like ‘granite’ cookware and ‘porcelain’ bathtubs or shower-surrounds

Plagioclase- rocks made up of plagioclase crystals are often used in cladding buildings. The Temple Main Campus Computer Building that you saw on the campus walking tour is covered with black plagioclase rock with blue-flash- butterflywing color that develops in the plagioclase as it weathers and forms some sub-microscopic clay particles in the crystals.

23 Quartz- has an electrical property called ‘piezoelectric’, because when a quartz crystal is squeezed, it generates an electrical microvoltage. Conversely, when you apply a microvoltage, it causes the quartz crystal to fluctuate or oscillate. The telephone has a slice of quartz crystal that converts the incoming signal in the wire into a vibration that plays in the earpiece. Conversely, when you speak your voice vibrations hit the quartz and generate the voltage that transmits through your phone to the party at the other end of the line. In much the same way oscillating a quartz crystal with a man-made-electric field allows us to make such devices as the so called ultrasonic cleaners or sonar generators, while squeezing or percussing a quartz crystal is the active mechanism in flintless fire starters and cigarette lighters

Olivine- This mineral has a very high melting point. As a result it makes a very good high temperature furnace lining in many industrial processes like making glass, copper or steel.

Talc-As a powder this has been used since ancient Egyptian times either a cosmetic and/or lubricant.

Garnet-The inside of almost all TV picture tubes has been frosted by sand- blasting with garnet powder to produce a screen for the projected images. Both quartz and garnet have no cleavage, quartz sand is usually taken from a river or beach where it has been rounded by abrasion. On the other hand, garnet abrasives are produced by breaking up the garnet crystals in a hammer-mill and so the fragments of garnet are very angular .Garnet sandpaper is superior for wood work as the wood fibers do not load up the angular grains as quickly as they do the rounded beach sand grains on the original-type of sandpaper.

Biotite/Muscovite Micas- The mica type minerals are used in three different areas of everyday life. Mica is stable to about 750oC(~1380oF) and thus it is a good electrical insulator. As you will discover in this lab, its cleavage fragments are flexible (1) Therefore it has been used historically to support electric heating elements such your toaster since mica can be cut with scissors and drilled to thread wires in and around it.(2) Mica has been used as the window in electrical fuses. (3) When heated beyond 700oC the mica loses the water in its crystal explosively, not unlike popping corn. As a result it expands into a flaky granule know to all of us as kitty- litter or vermiculite for potting flowers.

24 Pyroxene- This mineral typically forms at high temperature from volcanic lavas. Since it is formed at high temperature (> 1000oC or >1830oF) it is very stable at high temperature . An iron-free form (proto-Enstatite) of pyroxene is the basic compound in Cornings PYROCERAM  cookware.

Amphibole- Not many commercial uses, but a stable, water-containing mineral to temperatures >900oC(~1650oF). Thus when it forms it may trap water in the deeper Earth and remain stable until it exceeds this temperature at which point the water is freed and such water may account for the steam that triggers volcanic eruptions like Mt. St. Helens in Washington in 1980 and 1982.

SULFIDES

Galena- A principle ore of lead. While lead is poisonous, many of its other properties are so unique that we depend for example on lead’s low melting point for use in solder for printed circuit boards, and as an alloying agent in bronze. Galena, itself was used in the first radios as the ‘catwhisker’ tuner as it is a natural semiconductor.

Pyrite- An iron sulfide, but not really an ore of iron due to environmental problems of sulfur dioxide and acid rain, particularly since Magnetite is a cleaner ore of iron. Pyrite is known as ‘fools gold’ or ‘black diamonds’ in the Pennsylvania Coal mines. Pyrite associated with coal became oxidized and produced historically over 500 miles of acidified streams running out of the coal mines in Pennsylvania. Burning such coal rich in pyrite also oxidizes the sulfur and causes acid rain. In this case, societal ’accidental’ releases of pyrite have had very negative impacts on our environment.

OXIDES

Corundum- With hardness =9 there are many abrasive uses in machine tool industry.

Hematite- Naturally occurring ‘rust’. Not so much an ore of iron, but a major red pigment in primer paints. After all, once it is ‘rusty’ what else can happen, so its use in paint is logical.

Magnetite- The major ore of iron without which we would not be living in the Steel Age. 25 26 CARBONATES

Calcite- With the heat treatment of rocks made of calcite(limestone) and the heat induced loss of carbon dioxide, we make Lime for use in agriculture as well as use in cement and concrete. Optical quality calcite single crystals have the ability to polarize light and so are used in microspcopes for this purpose.

Dolomite- Rocks made up of a great deal of dolomite are called dolostones. Many thousands of tons of dolostone are used in the Philadelphia area (mined out near Norristown on Chemical Rd.) for road construction gravels.

HALIDES

Halite- Table salt is the refined (to take out clay and bacteria) form of this mineral that originally forms by evaporation of sea water. Ice control in the winter is another critical usage of this mineral just as it comes out of mines in New York and is hauled here.

Fluorite- Essentially the source of all the fluoride used in fighting tooth decay. Also when of optical quality, fluorite crystals are used for a more chemically durable lens material than glass.

SULFATE

Gypsum- A hydrated mineral which when first dehydrated by heating to temperatures greater than 390oC(735oF) and then remixing with water becomes the famous Plaster of Paris for medical cast uses and dry wall production in the building industry. The name, Plaster of Paris come historically from a Gypsum quarry near Paris where this was first prepared.

27 TABLE 1.

H6 Light No cleavage OLIVINE Green, H =6.5-7, L=vitreous G=3.3-3.4

QUARTZ Variable colors, concoidal fracture H= 7, L=vitreous G = 2.65

Cleavage ORTHOCLASE Pink-white C:2 planes at nearly rt angles H=6 G=2.6

PLAGIOCLASE Dk Gray- white C:2 planes at nearly rt angles planes may show striations H=6 G=2.6-2.75

H6 Dark No Cleavage CORUNDUM Gray-pink may have hexagonal prisms H=9 G=4.0

GARNET red-red brown hackly fracture H=6.5-7.5 G=3.5-4.3

HEMATITE red to black, streak=red may be granular H=5-6 G=5.3

MAGNETITE black, streak=black strongly magnetic H=6 G=5.2

Cleavage PYROXENE green-black C:2 planes at rt angles H=5-6 G~3

AMPHIBOLE green black C:2 @60o and 120o H=5-6

H6 Metallic PYRITE brassy, fool’s gold, cubes common H=6-6.5 G=5.0

28 TABLE 2.

H6 Light No Cleavage TALC greenish white soapy feel, may be flaky H=1 G=2.7

Cleavage HALITE colorless to white salty taste; water soluble C:3, cubic H=2 G=2.2

GYPSUM white to transparent occasionally flexible platelets C=1, tabular H=2 G=2.3

CALCITE white, tan, green, yellow DOLOMITE tan to pink to white Calcite shows HCL soluble with fizz of CO2; Dolomite fizzes in acid only if powdered first C:3 rhombohedral H=3 G=2.7

FLUORITE. Highly variable(blue,purple) C:4 octahedral H=4 G=3.2

MUSCOVITE silvery to transparent Flexible cleavage fragments C:1 perfect H=2-3 G=2.75-3.0

H6 Dark No Cleavage NO SAMPLE IN LAB

Cleavage BIOTITE Black-brown Flexible cleavage fragments C:1 perfect H=2-3 G=2.75-3.0

APATITE Green, brown, blue C:1 poor basal H=5 G=3.1

H 6 Metallic GALENA silvery to dull C:3 cubic H=2.5 G=7.6

29 30 31 Questions

1.) Why is coal not a mineral?

2.) Is snow a mineral? Why or why not?

3.) Is glass a mineral? Why or why not?

4.) The gem, sapphire (birthstone for September), and the gem, ruby (birthstone for July), are both simply colored varieties of corundum. The blue of sapphire is caused by iron and the red of ruby is caused by chromium, but basically the crystals are still aluminum oxide. Why do these gemstones make such good durable jewelry and rings ? From the listed properties of corundum in Table 1, discuss at least two different reasons.

5.) Blue topaz has enjoyed a fad-popularity to the extent that it is ‘the gem of the 90’s’, available in many stores and catalogues. While usually much cheaper than sapphire, the topaz crystals have perfect basal cleavage (one plane). Despite its being cheaper, would it be as good an investment as a similar sapphire ? Why?

6.) Lime-green Peridot is the gem name for olivine and it is the birthstone for August. Examine Tables 1 and 2. Of the minerals listed that can be green why is peridot the best choice for jewelry or a ring ?

7.) Several colors of quartz are possible, each with its gemstone name: Smoky quartz=black and transparent as the name implies; amythest=purple (birthstone for February); citrine=yellow-brown (a contender with yellow- brown topaz for the birthstone for November). Since quartz is fairly abundant relative to other gemstones, it usually beats them out just on price 32 alone. But what two properties of quartz make it additionally sensible for jewelry?

8.) Which sandpaper would be best for steel…the original tan (quartz) sandpaper, the ‘red’ sand paper (garnet), or the white sandpaper (corundum)? Why?

9.) After reading the provided page(s) of mineral usages, make a list and count how many times you have used these 20 minerals in your life today.

10.) Take an unknown sample(s) given to you by your TA and work through the flow chart for additional practice. Use the blank chart in the lab manual to fill in information for mineral identification.

MINERAL IDENTIFICATION CHART

No. Minerals Hardness Cleavage Streak Luster Others 1 2 3 4 5 6 7 8 9 10 11 12