19. What mineral substances are MOST rocks made of?
Most rock-forming
minerals are silicates (oxides of the element
silica). About 90 percent of Earth's crust is composed of silicate
minerals. Quartz is the most common form of silicon dioxide. It makes up most of the sand at the seashore, occurs as a rock in the form of sandstone, and quartzite, and is an important constituent of many other rocks such as granite and gneiss.
There are many varieties of quartz and those that occur in distinct crystals are named chiefly according to their color, for example: rock crystal is clear and colorless; smoky quartz has probably darkened as a result of exposure to radioactivity; amethyst crystals are purple; citrine is a light yellow crystal; rose quartz is pale to deep pink.
Other silicate rock forming minerals, such as the feldspars (which like quartz are found in most igneous rocks like granite and gneiss) are silicates of aluminum with potassium, sodium, and calcium.
20. Are some minerals harder than others?
Yes. A German mineralogist, Friedrick Mohs (1773-1839) developed a very practical mineral scale of relative hardness. He listed ten minerals ranging from 1. talc (the softest) to 10, diamond (the hardest).
On Mohs' scale of hardness a mineral with a value up to 2.5 can be scratched with a fingernail, up to 4 can be scratched with a coin, and up to 6 by a knife.
The minerals used by Mohs to establish his scale were: 1) talc; 2) gypsum; 3) calcite; 4) fluorite; 5) apatite; 6) orthoclase; 7) quartz; 8) topaz; 9) corundum; 10) diamond.
21. What about ruby and emerald. Are these minerals?
Yes. Emerald (beryl - beryllium aluminum silicate), ruby (corundum - aluminum oxide), sapphire (corundum), opal (silica) and diamond (carbon) are all minerals and have been highly valued by people over the ages because of their rarity and their beauty. Diamond is highly valued by modern societies but historically has been valued less than the more colorful minerals. Most natural diamonds come from Africa but they are found all over the world. Small, synthetic diamonds can now be made and are used in industry where hard cutting edges are needed.
True emeralds are a deep green and a large, flawless emerald is more valuable than a diamond. The finest rubies come from Burma, and most opals come from Australia.
22. How do scientists classify/organize minerals?
Minerals are grouped/organized/classified by scientists in several different ways depending upon the properties the scientists want to emphasize in different contexts. For example, minerals whose molecules contain the metal element iron (such as hematite, magnetite, siderite) can be grouped together as can be the zinc minerals such as sphalerite, smithsonite, willemite.
However, a mineralogist might prefer a classification based on the type of compound and its properties and so would group minerals together that have similar chemical composition even though they contain different
elements. For example a carbonates group would include both siderite (iron carbonate) and smithsonite (zinc carbonate) which would not be grouped together if they were being classified according to the metal element in the molecule (iron and zinc are both metal elements.)
23. What are Native Elements?
These are chemical elements that are found in nature in their native (uncombined) state. Most elements do not exist in nature as elements but instead are always found as compounds - each molecule being a combination of several elements. There are three groups of elements that are found in nature in their native state: 1) a few metals such as gold, silver, copper, platinum and iron; 2) a few semi-metals such as arsenic, antimony, and bismuth; and 3) a few non metals such as carbon, and sulphur.
24. What is ore?
An ore is a mineral or rock from which a metal and certain other substances can be extracted for commercial purposes. Sometimes ametal is present in its native form; gold and platinum are found this way. Almost always however the metals occur as oxides, sulphides, sulphates, silicates etc. and the metal has to be extracted from its ore (separated from the other chemical elements) by chemical means.
The branch of applied science that is concerned with the production of metals from their ores is metallurgy.
25. Which is the most abundant metallic element in Earth's crust?
Aluminum - called aluminium in some parts of the world.
While aluminum is the most abundant metallic element in the Earth's crust it is not the most abundant 'element'. Oxygen is the most abundant element followed by silicon and then aluminum.
Most of the aluminum is physically and chemically bound inside rocks that comprise Earth's crust. However in some areas (largely under tropical conditions in Australia, Guinea, Jamaica, Russia, Brazil, and Surinam) those rocks exposed at the surface have weathered and broken down into bauxite which is the chief ore of aluminum. Bauxite is a claylike amorphous substance from which aluminum can be extracted.
Aluminum is a very light, very strong metal and is used in circumstances where lightness is as important as strength.