Download Rock Identification Lab

Name ______________________________
Rock Identification Lab
Mineral Hardness
Objective: You will determine the relative hardness of common objects relative to the known hardness
of index minerals. We will use fingernail, copper, glass, and ceramic.
Determine the hardness of each object by finding which minerals will scratch it, or alternatively,
whether or not the object can scratch the mineral.
Softer
Harder
Approximate Hardness
Fingernail
Glass
Copper
Ceramic
2. Name:
a. two minerals that have a hardness greater than glass
(1) _________________________________
(2) _________________________________
b. one mineral that would scratch copper, but not ceramic
(1) _________________________________
c. two minerals that you could scratch with your fingernail
(1) _________________________________
(2) _________________________________
3. Name a mineral, besides diamond, which could be used to cut glass.
________________________________________________________
4. How would knowing the relative hardness of a mineral be useful to a geologist?
1
Minerals
A mineral is a naturally occurring inorganic substance with a definite chemical composition and a regular
internal structure. Most minerals are crystalline. Rocks are composed of one or more minerals.
Property
Hardness
Definition
Resistance to scratching or
abrasion
Cleavage
or
Fracture
Breakage of a mineral
along planes of weakness
or in rough pattern
Luster
Color
Character of the light
reflected by a mineral
Reflected visible light
How to Evaluate
Use minerals of known hardness from the Mohs Hardness
Kits. Scratch the unknown mineral with a known hardness
to determine which mineral is harder. We only need an
approximate hardness value.
Examine the mineral for areas where the mineral is broken.
Look for areas where the light reflects from planar surfaces
(cleavage) or the breakage is either irregular or has the
appearance of broken glass (fracture).
Look at the sample to determine if the mineral is metallic in
appearance (opaque and shiny) or non-metallic .
Estimate the color - white, black, green, clear, etc.
Minerals to Identify in this Lab
Mineral
Pyrite
Kyanite
Gypsum
Magnetite
Quartz
Muscovite mica
Talc
Feldspar
Galena
Luster
metallic
non-metal
non-metal
metallic
non-metal
non-metal
non-metal
non-metal
metallic
Hardness
6.5
4
2
5.5-6.5
7
2-2.5
1
6
2.5
Clev/Frac
fracture
cleavage
fracture
fracture
cleavage
cleavage
cleavage
cleavage
Common Colors
brassy yellow
Blue,green,grey,white
milky, pink to grey
black to silver
clear, pearl, variable
clear to yellow
white to green
clear, cloudy, pink
metallic silver
Other
fool’s gold, glassy
long crystals
scratch w/fingernail
magnetic
glassy fracture
thin sheets
greasy feel
high density
Fill in the table using numbered samples from the box marked “Luster”
Sample
1
2
3
4
6
8
11
14
15
Luster
Hardness
Clev. or Frac?
Other
2
Name
Igneous Rocks
Igneous rocks solidify from molten magma and lava. Cooling and crystallization can occur beneath the
surface (plutonic) or on the surface (volcanic).
Property
Texture
Color
Density
Vesicles
Dark Minerals
Definition
For igneous rocks, refers
to the crystal size
Reflected visible light
Weight per volume
Voids from air bubbles
Mafic has more than 40%
How to Evaluate
Glassy (non-crystalline), Coarse(can see mineral grains),
Fine (cannot see grains)
Note if color is light, medium or dark
Compare equal size rocks, heavier is more dense
Open voids permeate rock
Estimate % of blackish crystals in rock
3
Igneous Rocks to Identify in this Lab
Scoria (Basaltic) – volcanic, black, porous texture, tiny grain size, variable density depending on porosity.
Look for vesicles (air pockets) in dark rock.
Granite – plutonic, generally light colored, lower density, hard, medium to coarse grained, no vesicles.
Look for quartz (white, pink), less than 40% dark minerals, lighter color,
Gabbro - plutonic equivalent of basalt, dark and may have greenish hues or somewhat shiny, high
density, medium grain. Look for dense rock and more than 40% dark minerals.
Ryolite – volcanic equivalent of granite, light colored, low density, fine grains often 2 sizes. Look for light
color, fine grain often with embedded larger crystals, gritty feel.
Basalt – volcanic, dark, more than 40% dark crystals, fine grain (smaller than gabbro), dense, most
abundant rock at the surface of the Earth and Moon.
Obsidian – volcanic, medium density, black, smooth glassy texture, no vesicles. Look for black, glassy,
sharp edges.
Andesite – volcanic, usually blueish-grey or grey, large (visible) and small (not visible) grains, medium
density. Look for lighter color, medium density, and smooth texture w/ larger crystal inclusions.
Fill in the table using numbered samples from the box marked “Igneous”
Sample
Texture
(coarse, fine,
glassy)
Vesicles?
yes/no
Light,
More than
medium, or 40% dark
dark color
crystals?
0
1
5
9
10
12
15
4
Density
(light, med,
heavy)
Name
Sedimentary Rocks
Sediment is deposited in a number of ways including movement by water, air, gravity or other erosional
agents, and by deposition in place through chemical and biological processes. Hardening of this material
results in sedimentary rock.
Property
Clastic
Chemical
origin
Definition
Obvious pieces of rock
(clasts) fused into a matrix
Formed in place by
chemical processes
Organic
origin
Formed in place by
biological processes
How to Evaluate
Observe clast size, Mixture (many sizes), coarse, medium
(sand), fine (smooth).
Chemical deposition usually results in a uniform mineral
throughout. Crystalline texture can range from course
(easily visible to the eye) to fine.
Biotic formation may show fossils (limestone) or black plant
material, such as coal or lignite.
5
Sedimentary Rocks to Identify in this Lab
Travertine (calcareous tufa) - limestone deposited from water in caves, lakes, streams, and percolating
groundwater, highly porous, off-white color, non-clastic (chemical deposition).
Halite (rock salt) – translucent crystalline salt, usually impregnated with colored impurities that can
result in many different colors, chemical deposition, soft hardness, look for salty taste
Sandstone – clastic, sand (barely visible grains), variable color and hardness, gritty feel. Look for gritty
feel (like sandpaper) and uniform, barely visible grains.
Bituminous Coal – non-clastic, organic origin, black color, low density. Look for black, low weight.
Fossil Limestone – chemical/biotic composition, fairly hard, generally light colored, smooth to rough.
Limestone may be smooth or, in fossil limestone, look for fossils of marine creatures.
Gypsum – chemical deposition, fine grain (gritty or sandy to touch), white color, bubbles under acid.
Look for uniform white color, hardness of 2.
Breccia - clastic, large clasts easy to see, mixed hardness, mixed color, rough to touch. Look for mixture
of clast sizes, including large fragments. Key feature is angular particles.
Conglomerate – large clasts of gravel and sand cemented together, fragments often rounded, matrix
material often light color, very rough to touch. Key feature is rounded particles.
Oil Shale – clastic, fine grain (cannot see grains) uniform texture, may show layers, fairly smooth to
touch. Look for smooth, banded or layered rock.
Fill in the table using numbered samples from the box marked “Sedimentary”
Sample
Clastic?
yes/no
Clast shape
(round, angular,
mixed, sand, silt
or clay)
Organic
origin?
(fossils, black)
1
2
3
7
10
12
13
14
15
6
Chemical
origin?
(uniform)
Name
Metamorphic Rocks
Metamorphic rocks have changed from their original form as igneous or sedimentary rocks due to
temperature and pressure or through chemical alteration.
Property
Texture
Definition
The relationship between
the materials of which a
rock is composed
Banding
Foliated rock layering
characteristic shape
Grain Size
How to Evaluate
Foliated textures show a distinct planar character. This
means that the minerals in the rock are all aligned with each
other. This planar character can be flat like a piece of slate or
folded. Non-foliated textures have minerals that are not
aligned. Essentially, the minerals are randomly oriented.
Look for layering in the rock, usually different colors. It can
be either linear (straight) or distorted (wavy).
Fine to coarse
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Metamorphic Rocks to Identify in this Lab
Gneiss – foliated, medium to coarse grained, hard, variable colors, rough to the touch. Often key
feature is distorted banding.
Garnet Schist – foliated, fine to medium grains (see by eye), hard, variable color, sometimes shiny, lack
banding. Look for quartz, mica, and/or garnet (red crystals) in rock.
Serpentine – non-foliated, medium grain, mixed hardness, contains dark to light green olivine crystals,
medium grain size; green and “scaly” appearance gives the name
Slate – foliated, very fine grain (cannot see crystals), hard and brittle, darker color, may contain mica
giving a sheen, feels fairly smooth, layering often visible.
Marble – non-foliated, medium grain includes soft minerals, all colors, gritty to the touch. Check
hardness, looking for soft minerals (may not even scratch glass, sometimes).
Graphite – forms from coal, dark color, dull sheen, fine grain, black residue to touch, scrape black
portion across paper to see if leaves a dark line like a pencil.
Quartzite – non-foliated, medium grain, very hard (6 or 7), pale colors, gritty feel like sand. Check
hardness (will scratch glass and ceramic), sandy feel.
Soapstone –foliated, fine grain, soft, generally grey/blue color, feels smooth and greasy. Can usually
scratch with fingernail and feels slippery.
Fill in the table using numbered samples from the box marked “Metamorphic”
Sample
Texture
(foliated,
non-foliated)
Banding?
Grain size
(coarse,
med, fine)
Feel (sandy,
(greasy,
smooth)
1
2
4
6
8
9
10
12
8
Other distinctive
feature
Name