Copy of Lab 02 Minerals and Rocks
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106
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Geology
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Dec 6, 2023
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GEOSCI/ENVIR ST 106: Environmental Geology
Lab 2: Mineral Identification and Intro to Rocks
Assignment overview:
Geologists often have to identify rocks and minerals based on prior
experience and knowledge while out in the field in remote environments, where few tools are
available. For this reason, you’ll often see geologists testing rocks’ weight, squinting at them
through hand-lenses, trying to break them on different sides, or using them to scratch whatever
they have around (pennies, nails, and pieces of glass are perennial favorites!). Scientifically,
what geologists are trying to do is examine the density, habit, cleavage, and hardness of the
minerals. While sometimes more sophisticated tools are necessary, many of the earth’s most
common minerals (including most silicates) can often be identified with the basic tools you’ll
learn in this lab.
Instructions (25 points total):
This lab requires you to watch videos showing off a series of
minerals and examples of testing their properties. Answer each question with a few words or 1-2
sentences maximum, unless otherwise specified. In cases where you use an online resource to
help you answer the question, provide links to any sources used. If you have any questions
about this assignment, contact a TA by email or during office hours. All questions to be
answered are marked by red highlighted fields (_________)
Submission:
To submit the assignment on Canvas, use the following steps:
1.
In Google Docs, generate a PDF: File → Download as → PDF Document
2.
In Google Docs, use Share → Get Shareable Link, and copy the link address
3.
In Canvas, upload your PDF to the assignment
4.
In Canvas, paste the link address to your Google Doc in the assignment comments.
1
Background
Geologists use many observations of hand samples to try to decode what minerals a rock might
contain. Along with these observations comes a fair amount of terminology that can be used to
describe samples. Below we review some of the terminology and tests that can be used to
identify a mineral. You should read through this section so that you are able to use this
terminology fluently in your descriptions.
Visual Properties:
Color: The color of the mineral in white light. Note that this is rarely definitive and can be
misleading! Many minerals appear in multiple colors. For example, quartz is often colorless and
translucent, but small amounts of impurities can turn it bright purple, at which point it is given
another name (amethyst), even though its crystal structure still implies it is quartz. Similarly,
other impurities can turn quartz pink, creating “rose quartz”, which still has the same essential
chemical structure.
Luster: Appearance of the surface in natural light, based on its texture and reflectance.
Examples terms include:
●
Adamantine (diamond-like brilliance)
●
Resinous
●
Greasy
●
Pearly
●
Silky
●
Metallic
●
Waxy
●
Vitreous (glassy)
Images with examples of these can be found here:
https://en.wikipedia.org/wiki/Lustre_(mineralogy).
Habit: appearance of a single crystal or manner in which crystals grow together in aggregates.
Some examples are:
●
Amorphous / Massive: No crystals or grains visible
●
Euhedral (Anhedral): Grains from perfect (imperfect) geometric shapes, like cubes,
rhombus, octagons, hexagons
●
Banded: Containing distinct color bands
●
Botryoidal / Globular: Forming round, ball-like shapes.
●
Foliated: Crystals Like pages of a book, i.e. like overlapping sheets or leaves that often
can be separated
●
Granular: Many interlocking grains of approximately the same size
●
Nodular / Oolitic: made up of many small rounded interlocking grains
●
Radiating: thin crystals growing outward from a single point
2
●
Specular: Reflecting, like a mirror ball
●
Tabular: Crystals shaped like small tablets
Physical Properties:
Beyond visual appearance, the physical properties of a mineral can be further tested by
examining its hardness, the patterns in which it breaks, and how it reacts to acid, magnets, and
UV light. These properties are, of course, not possible to test from photos alone, but it is
important to know that these are the properties that geologists rely on when visual appearance
isn’t enough to definitively identify a mineral.
Hardness: The resistance that a smooth surface of a mineral offers to scratching. Hardness is
rated on “Mohs’ Hardness Scale”, which ranges from 1 to 10.
Mohs Scale
Simple Test Materials
1. Talc
2. Gypsum
finger nail (2.5)
3. Calcite
copper penny (3.5)
4. Fluorite
5. Apatite
steel knife or nail (5-6)
6. Orthoclase (a feldspar)
glass (5-6)
7. Quartz
Streak plate (6.5-7)
8. Topaz
9. Corundum
10. Diamond
Streak: The color of finely powdered mineral (produced by scratching on a ceramic plate).
Streak color can often be substantially different from a mineral’s visual color, and is often more
indicative than observed crystal color. Note that some minerals will not produce a streak
(especially if they are quite hard!).
Cleavage & fracture: how a mineral separates into pieces or breaks. Only a few examples tend
to be distinctive:
●
Platy cleavage: separating along flat sheets (e.g., mica, biotite)
●
Cubic cleavage: Breaking easily into cubes (e.g., pyrite)
●
Conchoidal fracture: Fractures into amorphous, curved ripples (e.g., obsidian)
●
Earthy fracture: breaks apart like dry dirt
Effervescence in weak acid: Gives off a gas (“fizzes”) when acid such as HCl is applied (e.g.,
calcite)
Density: Mass of a mineral per volume
Magnetism: A few minerals (mainly those containing
iron) are attracted to magnets.
3
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Mineral
Color
Hardness
Other characteristics
Amphibole
(set of
minerals)
green, blue, black, brown
5-6
often forms needlelike crystals, two good
cleavages forming 120-degree angles
Calcite
variable; colorless if pure
3
effervesces (fizzes) in weak acid
Feldspar (set
of minerals)
white to gray or pink,
orange
6
two good cleavages forming a 90-degree
angle
Galena
silver-gray
2.5
metallic luster; cleaves into cubes;
high density
Halite
colorless
2 - 2.5
salty taste: cleaves into cubes
Hematite
red or dark gray
5.5 - 6.5
red-brown streak regardless of color
Kaolinite
white
2
earthy luster
Magnetite
black
6
strongly magnetic
Mica
colorless (Muscovite) or
black (Biotite)
2 – 2.5
cleaves into thin sheets
Pyrite
bronze-yellow
6 – 6.5
metallic luster; black streak
Quartz
variable; colorless if pure
7
glassy luster; conchoidal fracture
Talc
white to grey-green
1
greasy or slippery to the touch
4
Mineral Identification
1 - 10. Using the information given above as well as any external sources you need to, fill in the
following table. For distinguishing characteristics, you may use a few words or a short phrase to
describe your reasoning (2 points each).
No.
Mineral Name
Mineral Group
Distinguishing Characteristics
1
__halite__
__silicate_____
__orange color/colorless, cleavage_______
2
__quartz___
__silicate____
__very glassy and clear, scratched glass_______
3
__feldspar___
__silicate___
__90 degree angles along the edges and was an
orange color_______
4
___calcite____
__carbonite___
__fizzed in HCl, mostly colorless _______
5
__koalinite___
___silicate____
__low hardness, clay like _______
6
__talc___
___silicate____
__low hardness, clay and sheet layers _______
7
__galena____
___sulfide____
__metallic, scratched by a nail _______
8
___pyrite___
__sulfide____
_metallic, and bronzy-yellow, fools gold________
9
__Magnetite__
__iron oxide___
_magnetic________
10
____Mica___
___silicate____
__sheet like thing layers, brownish color _______
Sources used (1 point): ___class powerpoints______
https://celestialearthminerals.com/product/crystals-minerals/halite-mineral-specimen/
http://everstoneminerals.com/feldspar/
11. While color is not a perfect identifier of minerals, it does often provide some valuable
information. In 1-2 sentences, what general trends do you see between mineral groups and the
associated mineral colors? (2 points)
____Quartz and calcite looked very similar in color but calcite fizzed under HCl and quartz
didn’t, therefore we knew which one was quartz and calcite. Kaolinite and Talc were also about
the same color so we mixed them up at first but then we had to use the shape and texture to
determine it was the other way around. _____
5
Rock Samples
12. Each of the rock samples shown represents an igneous rock -- i.e. a rock that formed either
by eruption of magma or cooling of an intruded magma body. In 2-3 sentences, describe
similarities and differences between the different samples, and provide a brief hypothesis as to
why they might all look so different. (2 points)
____They all formed under different pressures which can change the outcome. Some also may
have had less time to form, maybe changing their shape and look. They all also have different
elements in them and these different elements may become different colors and when
interacting with other different elements can form something new. Some samples are clear and
others are opaque, like kaolinite and quartz. While quartz looks very different from kaolinite it
looks similar to halite as in they are both clear even when they have color to them_____
6
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