Guidelines for Mineral and Rock Collections

| Mineral List | Rock List | GNSC 320 Syllabus | Course Schedule |

• "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 Excursion

Store specimens separately

Keep specimens separated, to protect them from wear and tear by harder companions.

• 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.

Keep specimens clean

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 or lichen.
• If drawers are not dustproof, keep specimens in plastic bags.
• 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.

Label specimens

• 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 box...
• 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!
  • Mineral list with descriptions

Describe specimens

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 list
  • See notes and explanations below for the mineral descriptions.
• 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 List
• 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 light.
  • 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 List
• 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

Notes 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 systems.

   

• Hardness:
  • 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 Mohs' scale.
  • 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 cells.
  • 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 scratch... __ 2.5 fingernail, paper __ 3.5 Copper penny __ 5.5 Glass __ 7 Porcelain streak plate (does not leave a streak)	The specimen is scratched by... __ 2.5 fingernail __ 3.5 Copper penny __ 5.5 Glass, knife blade __ 6.5 Hardened nail __ 7 Porcelain streak plate (leaves streak mark)
  Mohs' scale __ 1 Talc __ 2 Gypsum __ 3 Calcite __ 4 Fluorite __ 5 Apatite __ 6 Orthoclase (potassium feldspar) __ 7 Quartz __ 8 Topaz __ 9 Corundum __ 10 Diamond

   

• Luster:
  • 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 hallway exhibit.
  • 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.

   

• Cleavage
  • 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 fracture instead.
  • 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, calcite).
  • How many cleavage planes are possible? Many; fluorite has 4; sphalerite 6.
  • Measure angles between cleavage planes with your protractor "goniometer."
  • How does cleavage differ from crystal form?
    • Cleavage occurs on parallel planes; crystal faces are rarely parallel.
    • 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 crystal.

   

• 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.

   

• Tenacity:
  • 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 go

   

• 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 marbles.
  • 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 and well-ventilated.
  • 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.