Common Rock-Forming Minerals - Earth and Space Sciences

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Examples of how a mineral surface reflects light for minerals with (A) good cleavage, (B) poor cleavage, <strong>and</strong> (C) fracture. Cleavage surfaces may be confused with crystal growth faces; in fact cleavage planes are sometimes parallel to growth faces. They can be distinguished as follows. (1) Growth faces are normally smooth, whereas cleavage planes, though also smooth, commonly are broken in a step-like fashion. (2) Some growth faces have fine grooves or ridges on their surfaces, whereas cleavage planes generally do not. (Plagioclase is an exception — it has striations on its cleavage planes.) (3) Finally, unless growth faces happen to coincide with cleavage planes, the mineral will not break parallel to growth faces. 5. Determine whether the flat faces on the following minerals are crystal growth faces or are due to cleavage. Specimen # Cleavage/Crystal Face 8 9 6. How many cleavage planes are there in the following minerals If there is more than one cleavage direction, what is the angle between cleavage planes (“NA”, “90°”, or “Not at 90°”) Specimen # # Planes Angle Between Cleavage Planes 10 11 12 13
7. Determine whether your fourteen mineral specimens have cleavage or fracture. (Remember, not all flat surfaces are cleavage planes; some are crystal faces. Use the characteristics described above to distinguish between the two types of flat surfaces.) If the mineral exhibits only fracture, write “fracture” in the column labeled "cleavage/fracture" on the mineral ID table. If the mineral exhibits cleavage, write the number of cleavage planes (1,2,3,4, or 6) <strong>and</strong> angle between planes (“NA”, “90°”, or “Not at 90°”) on the mineral ID table. If the mineral exhibits crystal faces, make a note of this in the “Other Diagnostic Properties” column of the table. Specific Gravity Specific gravity is a measure of relative density. It is determined by comparing the mass of a material to the mass of an equal volume of water. A mineral with a specific gravity of 3.0 would be three times heavier than an equal volume of water. Specific gravity is not expressed in units of any kind, as it is a ratio. specific gravity = mass of mineral mass of equal volume of water Specific gravity can be measured by using Archimedes' principle, one of the fundamental principles of physical science. Archimedes noted that a specimen weighs less when immersed in water than it does when weighed in air. He noted further that the loss of weight in water (weight in air minus weight in water) is exactly equal to the weight of the displaced volume of water. Therefore, the equation above can be rewritten as: specific gravity = weight of mineral in air weight in air minus weight in water 8. Using the hydrometer (directions are included), determine the specific gravity of the following minerals: Specimen # 5 Weight of Mineral in Air (grams) Weight of Mineral in Water (grams) Weight in Air Minus Weight in Water (grams) Specific Gravity 14 Other Properties Magnetism - Some minerals, such as magnetite, are attracted to magnets. Taste - Some minerals have a characteristic taste. For example, halite tastes like salt. Acid reaction - Some minerals that contain carbonate (CO3) will react with diluted hydrochloric acid (HCl), forming carbon dioxide (CO2) gas bubbles. Calcite (CaCO3) will react with HCl. Feel - Some minerals, such as talc, feel soapy or greasy. Presence of striations - Some minerals, such as pyrite, have closely spaced fine grooves on their crystal faces.
Page 1 and 2: ESS 103 Lab 2: Common Rock-Forming
Page 3: Cleavage and Fracture Cleavage is t
Page 7 and 8: Distinguishing similar-looking mine
Page 9 and 10: Use: First Measurement: Add weights
Page 11 and 12: Luster & Color Relative Hardness Ta

Common Rock-Forming Minerals - Earth and Space Sciences

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