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Vocabulary for Investigation 2: Scratch Test
1) Hardness- a mineral property that refers to the resistance of a
mineral to being scratched; minerals can be ordered by hardness.
2) Quartz- one of the most common minerals in Earth’s crust. It is
composed of silicon and oxygen and is probably best known as
beautiful, colorless, hexagonal crystals. Quartz also comes in
white, pink, purple and gray. Some sandstones and the rock
quartzite are almost 100% quartz. Quartz cannot be scratched with
a paper clip and has a glassy luster. Some colored forms of quartz
are valued as gems. (Hardness = 7)
3) Fluorite- comes in a variety of colors, including white, blue,
green and violet. Fluorite can be scratched with a paperclip. It
usually fluoresces or glows under an ultraviolet light source. It is
used to make high-octane gasoline and as a fluid slag in making
steel and smelting other ores. (Hardness = 4)
4) Calcite- another of the most common minerals on Earth.
Calcite’s chemical composition is calcium carbonate. Calcite can
be scratched with a penny. It is the major mineral in such common
rocks as limestone and marble, which are valued as building
materials. The presence of calcite can be detected reliably by
placing it in diluted acid and observing the formation of carbondioxide bubbles. (Hardness = 3)
5) Gypsum- a mineral that forms when seawater evaporates under
arid conditions. Its chemical name is calcium sulfate when it
combines with water. If the water is not present, the mineral is
anhydrite. Gypsum can be scratched with a fingernail and has a
pearly, glassy and sometimes fibrous luster. Heating gypsum
drives out part of the water. The whit powder that remains is what
we call plaster of Paris. Crushed gypsum is used in agriculture,
added to the soil as “land plaster” to neutralize alkaline soils.
(Hardness = 2)