June 12, 2005

Birthstone Report

We had to do reports on our birthstones in science class this year...yup.


Gems and birthstones are used for a number of decorative purposes. They can be found in earrings, necklaces, and bracelets. They adorn shelves in gift stores just about anywhere you go. But what are they really? They are just ordinary minerals that, throughout time, have been accompanied by myths and legends transforming them into lucky stones. A mineral, according the Encarta Reference Dictionary, is “an inorganic solid substance that occurs naturally in rocks and in the ground and has its own characteristic appearance and chemical composition.” This means that a mineral is a piece of matter that this not made up of living, or once living, materials. One good example of this is turquoise.
Turquoise is the birthstone for the month of December. Its bluish green color is determined by the amount of iron and copper in the area of the mine. When too much iron is in the area it causes the turquoise samples to become more greenish, causing the value of the stone to decline. The most expensive pieces of turquoise are known to come from Neyshābūr, Iran, but it is also mined in northern Africa, Australia, Siberia, and the southwestern United States.
Although color can be characteristic of a certain mineral it is also very important to recognize the luster of the stone. Luster is the quality of light being reflected from the mineral. There are many different categories of luster. To name just a few of the classifications of luster, are waxy, metallic, dull, pearly, glassy and silky. The luster of a certain mineral can often be hard to define, because it may be just one classification, two or somewhere in between. Turquoise has a waxy luster, meaning that it lets of a faint shine, similar to the way candle wax might look, thus giving it the name waxy.
A chemical formula for a mineral reveals every element in its makeup. In a formula each number and letter stands for something that helps build the material. Letters represent different elements and the numbers indicate how many atoms of that one element are in the formula. Turquoise for example has the chemical formula of CuAl6(PO4)4(OH)84H2O. Just from looking at the formula it is easy to tell what is in the mineral. Turquoise contains the elements of copper (Cu), aluminum (Al), phosphorous (P), oxygen (O) and hydrogen (H). The numbers following the elements in subtext show how much of that element is in the formula. For example in turquoise there are six aluminum atoms in the formula. When there are no numbers following the element it simply means that there is only one atom of that element at that part of the formula.
Every mineral has a property called hardness. Hardness is just what it sounds like, how hard the mineral is. The harder it is the more resistant it is to scratching and etching. When testing a mineral for hardness it can be either scratch on another mineral or material, or be scratched by another material. Either way it is done a scale of hardness needs to be determined. This can be done by using minerals that are already familiar using them to scratch the mineral being tested, or by using the Mohs hardness scale. The Mohs hardness scale, determined by Friedrich Mohs, sets certain minerals to a scale ranging from one to ten, one being the softest and ten being the hardest. The scale is as follows: talc is 1, gypsum, 2, calcite, 3, fluorite, 4, apatite, 5, orthoclase, 6, quartz, 7, topaz, 8, corundum, 9, and diamond being 10. All minerals fall somewhere along this scale. One way to test them is by using common items, such as knife blades, glass, coins and fingernails. Just as all minerals have a place on the scale so do the objects that are testing them. A fingernail is about 2.5, a penny, 3.5, a knife blade or a nail fall between 5 and 5.5, while a piece of glass can be scratched with minerals with a hardness of six or higher (scratches a mineral with five or lower). Turquoise has a hardness between five and six.
The crystal structure of a mineral is equally as important as the other characteristics of a mineral. Crystal structure defines how the atoms are arranged within the mineral, and how the axes of the mineral are set. There are six different types of crystal structures, or systems. They are isometric, tetragonal, hexagonal, monoclinic, orthorhombic and triclinic. A mineral may not always have a crystal structure, but many do. Turquoise has a triclinic system. In a triclinic system, such as the one that occupies turquoise, the axes are all of different length and sloped. The unevenness of the axes
creates a diamond, or kite, shape for the mineral as opposed to a square or and other shape.
Specific gravity is the density of an object divided by the density of a different object, called a standard. Ordinarily the standard is water. Turquoise has a specific gravity between 2.6 and 2.83. This means that the density of turquoise, 2.60-2.90 divided by the density of water, 1 g/cm³ is between 2.6 and 2.83.
Minerals always have a place where they can most likely be found. This is called its origin and environment. This includes where it is found, and any other minerals that it is commonly found with. Turquoise is sometimes found with quartz, an igneous rock.
Cleavage and fracture describe how the rock is broken. If a rock is broken so that is has flat plains then it has cleavage if it is uneven then it has fracture. Many minerals have both. Turquoise, however, has only an uneven fracture.
Though turquoise does not have any special properties, such as magnetism or double refraction, it has been used as a sign of mythology and worship for many civilizations around the world. In ancient Egypt tombs were filled with turquoise statues or servants that were believed to be servants of the dead in the after life. They also had a goddess that only looked over the turquoise mine and the surrounding desert. In the Aztec culture turquoise was believed to be the weapon Huitzilopochtli, the sun god, used to kill his sister. To the Navajo is represented a goddess of the sky. Then, just as it is now, turquoise is too soft for intricate and detailed works, so it is mainly used as insets in necklaces and other jewelry.
Turquoise has been a favored and important gem to many ancient nations and cultures all around the world. Now its meaning has changed and it is commonly used for jewelry, but it still carries what it has always been prized for, its pure blue color.

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