Guidelines for Mineral and Rock Collections
- "He who with pocket-hammer smites the edge
Of luckless rock or prominent stone, disguised
In weather-stains or crusted o'er by Nature.
The substance classes by some barbarous name,
And thinks himself enriched,
Wealthier, and doubtless wiser than before."
William Wordsworth, The
Keep specimens separated, to protect them from wear and tear by
- Plastic storage boxes work well and are relatively inexpensive
(sold at Wal-Mart for nuts and bolts, etc.). Sturdy steel or
wooden drawers are best. Do not use egg cartons: they are too
fragile, and rocks tend to slide around and mix together.
- If you must use egg cartons or similar arrangments, put the
specimens in plastic bags to keep them together. Cover each layer
with bubble wrap to ensure their integrity.
Dust hides their appearance.
- Gather only clean specimens that display their true character;
use a geologist's hammer to chip away surface weathering or moss
- If drawers are not dustproof, keep specimens in plastic
- If specimens are dusty, wipe them clean or dust them off. Use
an old toothbrush to clean them, if necessary.
- Consult a field guide for more extensive cleaning
recommendations, if necessary.
- Mark each specimen with a spot of white enamel paint, then
label it with permanent ink...
- Or place a label underneath each specimen in its compartment
- Or label its drawer...
- Or put each specimen inside a plastic bag, and affix a label
to the bag.
- Just label them somehow that's clear and obvious!
On a computer or in a notebook file, complete a catalog entry for
each specimen by filling out the appropriate template:
- Mineral template
- Compare your descriptions with the Mineral
- See notes and explanations below for the mineral
- Sedimentary template
- Note: When completing a description of a sedimentary rock
with this template, first fill out the cells in the right hand
column, including the Classification of the rock as
Detrital, Organic, or Inorganic Chemical. Then, depending on
the classification of the rock, fill out only one of the three
sections in the left hand column; i.e., for a Detrital rock
like Conglomerate fill out only the Detrital section and leave
the Organic and Inorganic Chemical sections blank. Rock
- Igneous template
- Composition: When the composition of an igneous rock
is not known (e.g., not listed in the tables in Chernicoff),
let the shade and color be your guide. That is, ultramafic and
mafic rocks are generally dark, felsic rocks are usually
- Classification: When the volcanic or plutonic
classification of an igneous rock is not known (e.g., not
listed in Chernicoff), let the texture be your guide. That is,
coarse-grained or phaneritic rocks are generally plutonic (or
intrusive), and aphanitic (fine-grained) rocks are usually
volcanic (or extrusive). Rock
- Metamorphic template
- Fabric and Shine:
- Foliated metamorphic rocks include schists (visible mica
flakes), phyllites (shiny without visible mica flakes),
slates (with slaty cleavage but no shine), and gneisses
(banded in alternating single-mineral layers).
- Nonfoliated metamorphic rocks include marble and
quartzite. The calcite crystals in marble impart a glitter
that should not be mistaken for mica.
- Texture and Fracture: Quartzite derives from
sandstone but has a quite different texture. Sandstone breaks
around the quartz sand grains, which results in a rough
texture, but in quartzite the surrounding matrix has become
hard enough that the rock breaks through or across the grains,
resulting in a much smoother texture. See Chernicoff for
definitions of other terms.
- Complete the hardness cell in the same way as for the
mineral template (explained below).
- Complete the metamorphic conditions cell by referring to
Chernicoff. Rock List
- Fossil template
and explanations for mineral descriptions
Refer to appropriate chapters of Chernicoff for definitions and
explanations of terms occurring in the templates. Points not
considered by Chernicoff are described below:
- Crystal form
- Use a magnifying lens to see little crystals.
- Measure angles with your protractor "goniometer."
- Refer to the handout for examples and diagrams of crystal
- Hardness refers not to how easily a mineral breaks (a
diamond is easily shattered with a hammer, despite being the
hardest substance on the Mohs scale), but to how easily it
scratches. Scratching measures the relative strength of the
mineral's atomic bonds. See Chernicoff for a discussion of
- Glass and steel occur in a range of hardnesses. Window
glass is around 5.5, and steel ranges from 5 to 6.5. A hardened
nail might be in the upper range, from 6 to 6.5.
- First perform the hardness tests with a streak plate,
copper, glass, nail, and fingernail, and when the results are
repeatable and consistent, record your results in the top two
- Finally, check the value on the Mohs' scale shown below
that corresponds to the hardness of the specimen. For example,
if a specimen will scratch copper but not glass, then its
hardness is between 3.5 and 5.5, and you would check 4 and 5 in
the Mohs' scale cell to show that its hardness is similar to
that of fluorite or apatite.
The specimen will
__ 2.5 fingernail, paper
__ 3.5 Copper penny
__ 5.5 Glass
__ 7 Porcelain streak plate (does not leave a
The specimen is scratched
__ 2.5 fingernail
__ 3.5 Copper penny
__ 5.5 Glass, knife blade
__ 6.5 Hardened nail
__ 7 Porcelain streak plate (leaves streak
__ 1 Talc
__ 2 Gypsum
__ 3 Calcite
__ 4 Fluorite
__ 5 Apatite
__ 6 Orthoclase (potassium feldspar)
__ 7 Quartz
__ 8 Topaz
__ 9 Corundum
__ 10 Diamond
- Luster refers to how a mineral reflects light, and is
either metallic (like pyrite and galena) or nonmetallic.
- Various degrees of nonmetallic luster are distinguished;
see examples of the various kinds of luster displayed in the
- Weathering and dirt can obscure a specimen's luster, so
specimens must be clean, fresh and competent.
- The luster of many gemstones is naturally dull; their
characteristic shine is due to polishing and faceting. Do not
use a polished specimen or surface to determine luster.
- Does the rock show signs that it would break evenly? Rough
surfaces are fractures; smooth and parallel surfaces are
cleavages. If no parallel surfaces are smooth, describe its
- Cleavage in 1 plane: produces parallel sheets, like
muscovite or biotite mica.
- Cleavage in 2 planes: breaks in two parallel planes, but
other surfaces are irregular fracture surfaces (e.g.,
feldspars, hornblende). Imagine a cube-shaped box. The top and
bottom are one cleavage plane. One side and its opposite side
represent a second cleavage plane. If the remaining side and
its opposite side are rough and irregular, then there is
cleavage in only 2 planes.
- Cleavage in 3 planes: breaks in three parallel planes, such
as a cube where all sides are smooth (e.g., galena,
- How many cleavage planes are possible? Many; fluorite has
4; sphalerite 6.
- Measure angles between cleavage planes with your protractor
- How does cleavage differ from crystal form?
- Cleavage occurs on parallel planes; crystal faces are
- Cleavage cracks may be visible one underneath another
(e.g., look at the sheets or layers within your biotite and
muscovite specimens). Crystals rarely have such repetitive
cracks or layers one within another.
- Cleavage of rocks is different from cleavage of
minerals: rock cleavage occurs between adjacent
mineral crystals or grains; mineral cleavage
occurs between adjacent atoms within a mineral
- Fracture: In some minerals the chemical bonds are of uniform
strength in all directions and cleavage does not occur. These
break in an uneven and irregular manner.
- Irregular = jagged
- Conchoidal = shell-shaped, like glass and quartz.
- Hackly = rough surface with sharp points
- Earthy = smooth and dull surface
- Splintery = fibrous
- Heft: A rough estimate performed in the field of the weight of
a sample compared to its size.
- Since a great deal of the earth's crust is quartz, its
specific gravity makes a convenient reference point: minerals
with a higher specific gravity are said to be heavy, minerals
with a specific gravity lower than 2.6 are said to be light.
Hold the specimen in one hand and a sample of quartz of
approximately equal size in the other hand. Record heft as
"heavy," "light," or "same as quartz."
- When a laboratory is available you may want a more precise
measure of the quantity of matter in the specimen. Instead of
heft, determine its density and/or
specific gravity. Specific gravity is the weight of the
specimen compared to the weight of an equal volume of water.
Density and specific gravity have the same numerical value,
differing in unit dimensions. Some minerals occur in varieties
with density ranges rather than a precise value.
- The specific gravity of quartz is 2.6, meaning that a chunk
of quartz is 2.6 times
heavier than an equal volume of water. You do not need to
determine the density or specific gravity of specimens in your
mineral collection unless it is necessary to distinguish them
from some other similar minerals with the same heft.
- Ductile: may be drawn out into a wire.
- Malleable: may be shaped or hammered into flat sheets
- Fragile: breaks when bent
- Flexible: Bends
- Elastic: Bends, but returns to original shape when you let
- Optical: Possible optical properties include transparent,
translucent, refraction, double refraction, fluorescence under UV
light, or phosphoresence (explained in Chernicoff). See the double
refraction display in the hallway exhibit.
- For classification and help with identification of specimens,
see hallway exhibit.
- Safety warning: acid test
- The acid-fizz test determines the presence of
CaCO3 crystals, as in calcite, limestones, and
- HCl = Hydrochloric acid, dilute (8%). Concentrated HCl is a
powerful and dangerous acid. The dilute solution used in your
rock test kit is not harmless, either, although it is only
an irritant much like vinegar.
- Do not inhale: it has an acrid odor and can irritate sinus
and lung tissue. It is not combustible, but do not expose it to
flame or excessive heat lest it vaporize and be inhaled. No
special ventilation procedures are needed if the room is large
- Do not expose it to your eyes: if contact occurs,
immediately flush eyes with running water (including under
eyelids) for 15 to 20 minutes. Contact physician if irritation
persists. Wear safety goggles if desired.
- Avoid prolonged skin contact. Flush affected areas with
soap and water. Contact physician if redness develops. Wear
rubber gloves if desired.
- Do not ingest. If conscious, drink large quantities of
water to dilute acid and seek immediate medical attention.
- Avoid contact with clothes: It may dissolve fabric. Do not
wipe hands on jeans. Wear lab coat if desired. Rinse and dry
specimen after testing.
- Wipe spills with paper towels; if necessary, neutralize
with baking soda (sodium bicarbonate) and flush down drain with
copious amounts of water.
- Safety warning: inhalation
- The serpentine group of minerals includes fibrous
substances that are hazardous when inhaled ("asbestos"). Your
collection includes a specimen of serpentine
wrapped in a plastic bag. Do examine its streak and hardness,
but do not test it for odor or taste.