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LAST NAME (ALL IN CAPS): ____________________________________ FIRST NAME: _____________________

5. MINERALS

Instructions: When you test a mineral for effervescence and you apply HCl, you must first ask permission from your instructor (remember

HCl is an acid and is hazardous to health). Some minerals that you would be working with may have sharp edges and corners, therefore, be careful when working with

them! When you are done with your lab work, please clean the desk and leave all materials you worked with in the same way you

found them! Your work will be graded on the basis of its accuracy, completion, clarity, neatness, legibility, and correct spelling of scientific

terms.

INTRODUCTION

Mineral: Naturally occurring, inorganic, solid, possesses orderly crystalline structure, and represented by a chemical formula.

PHYSICAL PROPERTIES OF MINERALS

COLOR A mineral’s color is usually its most noticeable property and may be a clue to its identity. Minerals such as galena, sulfur, olivine and gold have each a typical color.

Galena gray; Sulfur yellow; Olivine green

Many other minerals show a range of colors: For example, quartz comes in the following colors: clear, white/milky, purple, gray/smoky, red/rose

CLARITY OF MINERALS: Clarity refers to a mineral’s ability to transmit light.

Transparent: clear and see-through, like window glass

Translucent: foggy, like looking through a steamed-up shower door

Opaque: impervious to light, like concrete and metals

MINERAL HABIT: A mineral’s habit is the characteristic crystal form(s) or combinations (clusters, coating, twinned pairs) that it habitually makes.

LUSTER refers to the way a mineral surface reflects light.

Minerals that shine like metals have metallic luster, all others have non-metallic luster. Examples:

• Metallic luster: new coins, knife, keys, jewelry, aluminum foil.

• Non-metallic luster: glass, candle, pearl, porcelain

STREAK is the color of a mineral or other substance after it has been ground to a fine powder. The easiest way to do this is by scraping the mineral against an unglazed ceramic plate (streak plate).

•Calcite – Color: white, pink, or clear; Streak: white

•Hematite – Color: black; Streak: brown

•Pyrite – Color: brassy; Streak = dark gray

If a mineral is harder than the streak plate (H=6.5), it will scratch the streak plate and make a white streak of powder from the streak plate.

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CLEAVAGE The tendency of a mineral to break (cleave) along flat, parallel surfaces (cleavage planes). Cleavage planes are surfaces of weak chemical bonding (attraction) between repeating parallel layers of atoms in a crystal. A mineral that possesses one cleavage has a pair of parallel smooth crystal faces (surfaces). If there are three such pairs of parallel and smooth faces, the mineral is said to possess three cleavages.

HARDNESS A mineral’s hardness is a measure of its the resistance to scratching. Please memorize all 10 minerals of the Mohs Scale of Hardness.

TABLE 1. Moh’s Relative Hardness Scale

SOFT

MINERALS

HARDNESS MINERAL COMMON OBJECT

10 Diamond

Streak Plate (6)

Glass, Knife blade (5.5)

Iron Nail (4.5)

Copper Penny (3) Finger Nail (2.5)

9 Corundum

8 Topaz

7 Quartz

6 Feldspar

HARD

MINERALS

5 Apatite

4 Fluorite

3 Calcite

2 Gypsum

1 Talc

OTHER (SPECIAL) PROPERTIES

REACTION TO ACID (Effervescence): The vigorous bubbling (fizzing) that results when calcite reacts with dilute HCl.

DOUBLE REFRACTION: refers to double image produced when you view an object through calcite.

MAKING GRAY MARK: Graphite (it’s the “lead” in pencils) is the only mineral that leaves grey mark on paper

STRIATIONS: these are thin parallel corrugations or stripes found on the cleavage surfaces of only two minerals, plagioclase

and pyrite

MAGNETISM: A property shown by magnetic substances when they are sufficiently magnetized. Magnetic substances attract

magnets and other iron objects. The mineral magnetite acquires strong magnetism when it forms. It is the only magnetic

mineral known.

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TABLE 2. Mineral Identification Charts (GROUPS I, II, and III)

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QUESTIONS

Q1. List the five characteristics a material must have in order to be considered a mineral.

i. _________________________________________________

ii. _________________________________________________

iii. ________________________________________________

iv. ________________________________________________

v. _________________________________________________

Q2. Use the geologic definition of a mineral to determine which of the items listed in the chart below are minerals and which are not. Check (√) the appropriate box. For substances that you say are NOT minerals, explain why not under the explanations column.

Q3. I) Name a mineral that always shows one color and can be identified solely on the basis of its color:

II) Say True/ False: Minerals are crystals that are always clear and see-through, like window glass.

Q4. Name the element/s or compound that make up each of the following minerals. Refer to the Mineral

Identification charts given in Table 2.

I) Quartz: ____________________________ II) Halite: _______________________________

III) Diamond: _________________________ IV) Calcite: _______________________________

Q5. What is the streak of each of the following substances? Refer to the Mineral Identification charts

given in Table 2, as needed.

I) Graphite (pencil “lead”): ___________ II) Wheat: ____________________

III) Salt: __________________ IV) Charcoal: __________________

V) Quartz: __________________ VI) Muscovite: _________________

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Q6. Determine whether the luster of each of the following materials is metallic or nonmetallic.

I) A brick: ______________ II) Butter or margarine: ____________

III) A seashell: __________ IV) Sharpened pencil lead: __________

V) Ice: ________________ VI) A mirror: ______________________

Q7. Determine the number of cleavage/s each of the following minerals possess.

Calcite: __________ Quartz: ___________

Muscovite: _________ Galena: ____________

Plagioclase Feldspar: ________ Talc: _________

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Q8. Using Table 1 (Mohs Hardness Scale) as your reference, if a mineral can be scratched by a knife blade but not by a wire (iron) nail,

I) What is the hardness number of this mineral on Mohs scale? _______________

II) Is this mineral hard or soft? _________

III) What mineral on the Mohs Scale of Hardness has this hardness? __________________

Q9. Using Table 1 (Mohs Hardness Scale) as your reference, if an unknown mineral is scratched by a piece

of quartz and is able to scratch a piece of fluorite. What is its hardness or possible range of hardness? Explain how you determined the hardness.

Q10. The mineral shown in the accompanying figure has scratched the glass. Which of the following minerals could it be? Choose and circle your answer/s. More than one answer may be possible.

A) Calcite B) Topaz

C) Quartz D) Gypsum

E) Fluorite

Q11. The two figures below show the same mineral. Based on the features you see in these two figures, determine the following:

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I) What is the luster of the mineral? ___________________

II) What is the crystal habit (geometric shape) of this mineral? _______________________

III) What can you say about the mineral’s hardness? Explain your answer.

IV) What is the geologic term used to describe the parallel groves (stripes) on the crystals? _________

V) Using your answers from I) to IV) above and the Mineral Identification charts given in Table 2,

what is the name of this mineral? ____________________________

Q12. Name one distinctive property for each of these minerals:

Magnetite: _______________________________________

Calcite: _________________________________________

Halite: __________________________________________

Q13. Describe a situation where using the streak to identify a mineral is the best course of action.

Q14. The picture below shows the results of two attempts to scratch a piece of glass with two different minerals. The one on the left has failed to scratch the glass, even with a vigorous scraping, the one on the right easily scratched it. In the blank spaces below, give 2-3 possible mineral names. Mark the most likely mineral for each in capital letters.

Mineral on the left: ______________________________________________________

Mineral on the right: ____________________________________________________

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Q15. For the 6 minerals provided by your instructor, determine the physical properties indicated for each.

If a physical property cannot be determined with the given tools or methods discussed in lab/class,

write “Can’t be determined.” For CLEAVAGE, write the # of cleavages present as 1, 2, 3, etc. If the

mineral does not have any cleavage, write “None.” For OTHER PROPERTIES use only the following

terms, when applicable: magnetism, striations, making grey marks on paper (like the lead in your pencil),

double refraction, effervescence. If none of these can be found on your sample, write, “None.”

SAMPLE # 4

LUSTER:

CLEAVAGE:

STREAK:

SAMPLE # 5

COLOR:

CLEAVAGE:

HARDNESS:

SAMPLE # 6

STREAK:

CLEAVAGE:

LUSTER:

SAMPLE # 8

HARDNESS:

CLEAVAGE:

OTHER PROPERTIES:

SAMPLE # 13

CLEAVAGE:

OTHER PROPERTIES:

SAMPLE # 14

CLEAVAGE:

OTHER PROPERTIES: