1. In order to be considered a mineral, a substance must exhibit the following characteristics: (1) be naturally occurring, (2) be solid, 3) possess an orderly crystalline structure, (4) have definite chemical composition, and (5) be generally inorganic.
2. A rock is a more or less hardened (lithified) aggregate of minerals and/or amorphous solids such as natural glass and organic matter.
3. The particles are electrons, protons, and neutrons. The latter two are heavy particles found in the nucleus of an atom. Electrons are tiny, very lightweight particles that form a “cloud” surrounding the nucleus. The mass and charge data are as follows:
proton — one atomic mass unit, 1+ electrical charge
neutron — one atomic mass unit, electrically neutral
electron — tiny fraction of one atomic mass unit, 1— electrical charge
4. (a) The number of protons — A neutral atom with 35 electrons has 35 protons. (b) The atomic number — The atomic number is 35, equal to the number of protons in the nucleus. (c) The number of neutrons — The mass number (80) is the sum of protons (35) and neutrons. Thus the nucleus contains 45 (80–35) neutrons.
5. An ion is produced when an atom either gains or loses one or more electrons and becomes either negatively charged (if electrons are gained) or positively charged (if electrons are lost).
6. Isotopes of an element have varying numbers of neutrons in the nucleus and, hence, different atomic weights.
7. Crystal form refers to the geometrically regular, external growth shape that minerals can exhibit if crystal growth is free and unobstructed by other minerals. (The crystal grows into a fluid-filled cavity, for example.) Most crystal growth in nature is obstructed (not free), so crystals showing their characteristic, geometric forms are not that common.
8. Impurities often cause the same mineral to have many colors. For example, fluorite can be purple, clear, yellow, etc., while quartz can be practically any color.
9. The hardness test might help you make a determination since diamond is the hardest mineral in nature.
10. Any mineral listed in Mohs scale (Table 1.9), corundum for example, will scratch softer minerals (those with lower hardness values) and will not scratch harder minerals. Corundum would scratch virtually all other minerals, diamond being the lone exception. Thus corundum is widely used in abrasives and polishing compounds.
11. The specific gravity of water is one by definition. Thus, equal volumes of water and gold would have their weights in the ratio 1:20. Since the 5 gallons of water weigh 40 pounds, the 5 gallons of gold will weigh almost 800 pounds (5 gallons × 160 lbs/gallon = 800 pounds).
12. The two most abundant elements in the Earth's crust (by weight) are oxygen (46.6 percent) and silicon (27.7 percent).
13. All silicate minerals have the silicon–oxygen tetrahedron as their fundamental building block. This structure consists of four oxygen atoms surrounding a smaller silicon atom.
14. Feldspars are by far the most plentiful group of silicate minerals, comprising over 50 percent of Earth's crust. Quartz is the second most abundant mineral in the continental crust.
15. Three nonsilicate minerals that are commonly found in rocks are calcite, halite, and gypsum.
16. Mineral reserves are identified deposits from which minerals can be extracted profitably. The concept of a mineral resource has a broader meaning. In addition to including reserves, it also includes known deposits that are not yet economically or technologically recoverable, as well as deposits that are inferred to exist but not yet been discovered.
17. One way a mineral deposit could become profitable to extract is through an economic change; for example, the demand for a metal may increase and cause a price increase. Also, if a technological advance allows the metal to be extracted at a lower cost, it may become profitable to extract and thus be reclassified as an ore.