Translations:Adventist Youth Honors Answer Book/Nature/Rocks & Minerals - Advanced/3/en
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3. Know two minerals that belong to each of the following crystal systems:
a. Isometric
The isometric crystal system (or cubic) is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in metallic crystals. Isometric crystals include
- Sodium Chloride (NaCl, common table salt)
- Gallium arsenide (GaAs) is a compound of two elements, Gallium and Arsenic. It is an important semiconductor and is used to make devices such as microwave frequency integrated circuits.
- Zirconium dioxide (ZrO2), sometimes known as zirconia, is a white crystalline oxide of zirconium. Single crystals of the cubic phase of zirconia are commonly used as a substitute for diamond in jewelry. Like diamond, cubic zirconia has a cubic crystal structure and a high index of refraction. Discerning a good quality cubic zirconia gem from a diamond is difficult, and most jewellers will have a thermal conductivity tester to identify cubic zircona by its low thermal conductivity (diamond is a very good thermal conductor).
- Lead(II) nitrate is a chemical compound, the inorganic salt of nitric acid and lead, with the formula Pb(NO3)2. It is a colorless crystal or white powder and a strong, stable oxidizer.
- Copper(I) oxide or cuprous oxide (Cu2O) is an oxide of copper.
b. Hexagonal
In crystallography, the hexagonal crystal system is one of the 7 lattice point groups (see Hexagonal_lattice). It has the same symmetry as a right prism with a hexagonal base. Hexagonal crystals include:
- Graphite, a form of pure carbon, used as a lubricant and as pencil lead.
- Apatite is one of few minerals that are produced and used by biological micro-environmental systems. Hydroxylapatite is the major component of tooth enamel.
- Quartz is the second most common mineral in the Earth's continental crust. It is made up of a lattice of silica (SiO2) tetrahedra.
- Beryl is a gemstone with the chemical formula Be3Al2(SiO3)6. The hexagonal crystals of beryl may be very small or range to several meters in size.
c. Tetragonal
Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base (a by a) and height (c, which is different from a). Tetragonal crystals include:
- Wulfenite is a lead molybdate mineral with the formula PbMoO4. It can be most often found as thin tabular crystals with a bright orange-red to yellow-orange color, sometimes brown, although the color can be highly variable. In its yellow form it is sometimes called "yellow lead ore".
- Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula (NH2)2CO. It was the first organic compound to be artificially synthesized from inorganic starting materials.
- Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4.