Name
Lab day & time

Geology 2, Spring 1977
PRELAB #1. MINERALS

This prelab assignment is due at the beginning of your lab session. You will not be allowed to participate in the lab if you have not completed this prelab exercise.
Bring this prelab, with answers filled in, and your text book with you to your lab.
Read about mineral identification in Chernicoff, Chapter 2 pages 29-41 and check out the following Mineral Identification Key. Answer the following questions.
1. Color. Is color a dependable characteristic to use when identifying minerals? Why or why not?

Why could some minerals be similar in color yet completely different in composition? Give some examples.

2. Luster. Find each of the following minerals on the Mineral ID Key and circle the type of luster it has. Find a photo of each in Chernicoff and write down its figure number. Do the "metallic" ones look metallic in the figures?

Mineral metallic or non-metallic? Figure #

halite

quartz

hematite

mica (biotite)

3. Streak. Streak is especially useful for sorting out minerals with metallic luster.
According to the Mineral Identification Key:
What color is the mineral hematite?
What color is its streak?
What color is pyrite?
What color is its streak?

According to Chernicoff, if a certain mineral has trace impurities, would
you expect the streak color made by the different colored samples to differ?

4. Hardness Find the Mohs Hardness Scale in Chernicoff.
According to the Mohs scale, what is the name of the hardest mineral of all?
What number is assigned to describe the hardness of this mineral?
For the following pairs, circle the harder substance of each pair:
quartz or calcite
corundum or orthoclase
gypsum or fingernail
calcite or fingernail
window glass or quartz

5. Cleavage and Fracture. The non-metallic minerals often reveal their identities by the nature of their broken surfaces. Find a figure in Chernicoff illustrating the cleavage or fracture surfaces of each of the following minerals.Find the minerals in the Mineral ID Key and tell how many different cleavage planes it commonly has: one good cleavage direction (sheet type cleavage), two, or three; or none (instead, fractures with a conchoidal fracture).

Mineral Figure # Cleavage

biotite mica

halite (table salt)

feldspar

galena

quartz

If quartz has no cleavage planes, why do samples of it often have shiny flat faces, e.g. in figs. 2-10 and 2-14?

6. Effervescence , the "acid test". If you drip some dilute hydrochloric acid on a rock and it fizzes, what mineral is that rock likely to contain?

7. Density or Specific Gravity or G. Typical minerals (and the rocks made from them) have a density between 2.5 and 3 grams/cm3. For example:
What is the density (or specific gravity) of quartz?
Metallic minerals (and the rocks containing them) often have much higher densities.
What is the density (or specific gravity) of
hematite (iron oxide)?
galena (lead sulfide)?
24-carat gold?

8. Mystery Minerals . Using the Mineral ID Key, figure out the likely identity of the following minerals.
a. This mineral has a metallic luster.
It has a greenish black streak and a brassy yellow color.
It scratches (i.e., is harder than) a knife blade.
It probably is

It is often called "fool's gold". Suggest an easy test to distinguish it from real gold.

b. This mineral is a common dark-colored mineral with non-metallic luster.
It has one perfect cleavage so that it is splittable into thin sheets.
It is dark brown in color. It probably is

c. This is a white mineral with non-metallic luster.
It can scratch your fingernail but can be scratched by your knife blade.
It breaks along three clear cleavage planes.
It fizzes when you drop acid on it. It probably is

MINERAL IDENTIFICATION KEY
(H=hardness, G=specific gravity)
(distinctive characteristics of individual minerals are in boldface

Procedure for Identifying Minerals
1. First decide if the mineral has a metallic or a non-metallic luster.
2. If metallic, use Table A of the Mineral Identification Key.
First determine the streak and color,
then use the other listed characteristics to refine and check your identification
3. If non-metallic, check general color - dark or light and use Table B or C.
Determine hardness relative to glass.
Examine the broken surfaces of the sample for cleavage faces.
Use the other listed characteristics to refine and check your identification.

A. METALLIC LUSTER

Color of streak Properties Mineral

black to gray silver gray; 3 directions of cleavage at 90°;
H = 2.5 ; G = 7.6 (very heavy) GALENA
PbS

black to gray black to dark gray; magnetic ;
H = 6 ; G = 6 (heavy) MAGNETITE
Fe3O4

black to gray gray to black; G = 2.3;
H = 1 (very soft, marks paper easily) GRAPHITE
C

greenish black brassy to golden yellow, may tarnish purple;
H = 3.5-4; G = 4.2 CHALCOPYRITE
CuFeS2

greenish black brass yellow; commonly in small cubes;
H = 6-6.5 (hard) ; G = 5 (heavy) PYRITE
FeS2

reddish brown silver to gray, may tarnish reddish brown;
earthy masses or steel gray crystals;
H = 5-6; G = 5 HEMATITE
Fe2O3

yellow yellow; H = 2.5-3 (soft, malleable) ;
G = 19.3 (very, very heavy) GOLD
Au

B. NON-METALLIC LUSTER; DARK COLOR

Hardness Cleavage Properties Mineral

2 cleavages at almost 90° dark green to black; blocky crystals or fibrous masses;
H = 6; G = 3.3 PYROXENE
(augite)
Ca, Mg, Fe, Al silicate

2 cleavages at about 60° and 120° dark green to black; long crystals or fibrous masses;
H = 5.5; G = 3.3 AMPHIBOLE
(hornblende)
Na, Ca, Mg, Fe, Al silicate

harder than glass absent; conchoidal fracture yellow-green to olive-green; granular masses or small grains;
H = 6.5-7 (but may crumble); G = 3.3-3.4 OLIVINE
Fe, Mg silicate

absent; conchoidal fracture red, brown, sometimes yellow; well formed isometric crystals;
H = 6.5-7.5; G = 3.5-4.3 GARNET
Fe, Mg, Ca Al silicate

absent; conchoidal fracture gray to gray-black or violet; transparent to translucent, vitreous;
H = 7; G = 2.6 QUARTZ
SiO2
(violet = AMETHYST)

1 perfect cleavage, splits into thin elastic sheets brown to black, sheets translucent;
H = 2.5-3; G = 3 BIOTITE
K, Mg, Fe, Al silicate

softer than glass 1 perfect cleavage; splits into thin flexible sheets green to dark green, sheets opaque;
H = 2-2.5; G = 2.8 CHLORITE
hydrous Mg, Fe, Al silicate

absent red earthy appearance; reddish brown streak;
H = 1.5 - 5.5; G = 5 HEMATITE
Fe2O3
(earthen form)

C. NON-METALLIC LUSTER- LIGHT COLOR

Hardness Cleavage Properties Mineral

2 cleavages at about 90°; Plagioclase: dark gray to white; striations on some cleavage faces;
Orthoclase: gray to white or salmon pink
H = 6; G = 2.5 FELDSPAR
(Plagioclase =
Ca, Na, Al silicate)
(Orthoclase =
K, Al silicate)

harder than glass absent; conchoidal fracture colorless, white, gray, pink; transparent to translucent, glassy; granular masses or 6 sided prismatic crystals
H = 7; G = 2.6 QUARTZ
SiO2
(silica)

absent; conchoidal fracture translucent to opaque, dull;
wide color range
H = 7; G = 2.6 CHERT
SiO2

absent; conchoidal fracture olive green or yellow green; small, glassy, translucent grains
H = 7 (but may crumble); G = 3.2-3.5 OLIVINE
Fe, Mg silicate

3 cleavages at 90° cubic crystals; colorless to white; salty taste
H = 2.5; G = 2.2 HALITE
NaCl

3 cleavages not at 90° rhombs; reacts with acid; colorless to white or yellow; may show double refraction
H = 3; G = 2.7 CALCITE
CaCO3

softer than glass 1 perfect cleavage, 2 good cleavages flexible plates; colorless to white;
H = 2 (scratched with fingernail); G=2.3 GYPSUM
CaSO4.2H2O

1 perfect cleavage; splits into thin, elastic sheets transparent sheets; colorless to light yellow
H = 2.5; G = 2.9 MUSCOVITE
K, Al silicate

absent white; earthy masses, resembles chalk;
H = 1.2, G = 2.7 KAOLINITE
hydrous Al silicate

Mineral	metallic or non-metallic?	Figure #
halite
quartz
hematite
mica (biotite)

Mineral	Figure #	Cleavage
biotite mica
halite (table salt)
feldspar
galena
quartz

Color of streak	Properties	Mineral
black to gray	silver gray; 3 directions of cleavage at 90°; H = 2.5 ; G = 7.6 (very heavy)	GALENA PbS
black to gray	black to dark gray; magnetic ; H = 6 ; G = 6 (heavy)	MAGNETITE Fe3O4
black to gray	gray to black; G = 2.3; H = 1 (very soft, marks paper easily)	GRAPHITE C
greenish black	brassy to golden yellow, may tarnish purple; H = 3.5-4; G = 4.2	CHALCOPYRITE CuFeS2
greenish black	brass yellow; commonly in small cubes; H = 6-6.5 (hard) ; G = 5 (heavy)	PYRITE FeS2
reddish brown	silver to gray, may tarnish reddish brown; earthy masses or steel gray crystals; H = 5-6; G = 5	HEMATITE Fe2O3
yellow	yellow; H = 2.5-3 (soft, malleable) ; G = 19.3 (very, very heavy)	GOLD Au

	2 cleavages at almost 90°	dark green to black; blocky crystals or fibrous masses; H = 6; G = 3.3	PYROXENE (augite) Ca, Mg, Fe, Al silicate
	2 cleavages at about 60° and 120°	dark green to black; long crystals or fibrous masses; H = 5.5; G = 3.3	AMPHIBOLE (hornblende) Na, Ca, Mg, Fe, Al silicate
harder than glass	absent; conchoidal fracture	yellow-green to olive-green; granular masses or small grains; H = 6.5-7 (but may crumble); G = 3.3-3.4	OLIVINE Fe, Mg silicate
	absent; conchoidal fracture	red, brown, sometimes yellow; well formed isometric crystals; H = 6.5-7.5; G = 3.5-4.3	GARNET Fe, Mg, Ca Al silicate
	absent; conchoidal fracture	gray to gray-black or violet; transparent to translucent, vitreous; H = 7; G = 2.6	QUARTZ SiO2 (violet = AMETHYST)
	1 perfect cleavage, splits into thin elastic sheets	brown to black, sheets translucent; H = 2.5-3; G = 3	BIOTITE K, Mg, Fe, Al silicate
softer than glass	1 perfect cleavage; splits into thin flexible sheets	green to dark green, sheets opaque; H = 2-2.5; G = 2.8	CHLORITE hydrous Mg, Fe, Al silicate
	absent	red earthy appearance; reddish brown streak; H = 1.5 - 5.5; G = 5	HEMATITE Fe2O3 (earthen form)

Hardness	Cleavage	Properties	Mineral
	2 cleavages at about 90°;	Plagioclase: dark gray to white; striations on some cleavage faces; Orthoclase: gray to white or salmon pink H = 6; G = 2.5	FELDSPAR (Plagioclase = Ca, Na, Al silicate) (Orthoclase = K, Al silicate)
harder than glass	absent; conchoidal fracture	colorless, white, gray, pink; transparent to translucent, glassy; granular masses or 6 sided prismatic crystals H = 7; G = 2.6	QUARTZ SiO2 (silica)
	absent; conchoidal fracture	translucent to opaque, dull; wide color range H = 7; G = 2.6	CHERT SiO2
	absent; conchoidal fracture	olive green or yellow green; small, glassy, translucent grains H = 7 (but may crumble); G = 3.2-3.5	OLIVINE Fe, Mg silicate
	3 cleavages at 90°	cubic crystals; colorless to white; salty taste H = 2.5; G = 2.2	HALITE NaCl
	3 cleavages not at 90°	rhombs; reacts with acid; colorless to white or yellow; may show double refraction H = 3; G = 2.7	CALCITE CaCO3
softer than glass	1 perfect cleavage, 2 good cleavages	flexible plates; colorless to white; H = 2 (scratched with fingernail); G=2.3	GYPSUM CaSO4.2H2O
	1 perfect cleavage; splits into thin, elastic sheets	transparent sheets; colorless to light yellow H = 2.5; G = 2.9	MUSCOVITE K, Al silicate
	absent	white; earthy masses, resembles chalk; H = 1.2, G = 2.7	KAOLINITE hydrous Al silicate