Sunday, 1 May 2011

Report Text_Gems and Stones

Gems and Gemstones

What Is a Gemstone? What Is a Gem?

Have you ever seen a diamond in a ring? An opal in a necklace? A pearl earring? Diamonds, opals, and pearls are types of gemstones. A gemstone is a mineral, rock, or organic material that is used for jewelry, ornamentation, or art. A gem, such as a diamond, is a type of gemstone that must be cut and polished for its beauty to be visible. Opals and pearls may be styled into jewelry or art without any cuts or polishing. They are gemstones, but not gems.
This pendant has cut and polished diamonds and an opal. Do you think the diamonds are gems or gemstones? What about the opal?
This pendant has cut and polished diamonds and an opal. Do you think the diamonds are gems or gemstones? What about the opal? Find out what the answers are by clicking on the photo above.
©Mark Somma

Where are Gemstones Found?

Gemstones occur in locations all over the world. Diamonds are found deep within the earth in a rock called kimberlite. Tourmaline and beryl are found in stream beds after they erode from surrounding rocks. And garnet is often found in a rock called gneiss, which has been heated to high temperatures.
Tourmaline comes in many colors and sometimes one crystal can have multiple colors.
Tourmaline comes in many colors and sometimes one crystal can have multiple colors. The tourmaline crystals attached to the quartz are tri-colored which means they are made up of three colors.
©Chris Ralph

How Can You Describe a Gemstone?

Gemstones are described by specific gravityhardness, and color. These are all features of minerals.

Specific Gravity

Specific gravity is a measure of how much heavier a mineral is than an equal amount of water. Tourmaline has a specific gravity of 3.03 to 3.25. This means that it is a bit more than three times as heavy as water.
MineralHardness
Talc1
Gypsum2
Calcite3
Fluorite4
Apatite5
Feldspar6
Quartz7
Topaz8
Sapphire9
Diamond10

Hardness

Hardness is the resistance of a mineral to scratching. Geologists use a measurement called Mohs’ scale to describe the hardness of a mineral.
You can see that topaz has a hardness of 8 on the scale. This means that a topaz is harder than anything except a sapphire or a diamond.

Color

How would you describe turquoise? You’d probably say it’s blue-green. Gemstones are described according to their color because it’s a useful characteristic. Diamonds are clear, but can be tinted yellow, pink, or even black from the presence of other minerals.
Rare and highly valuable diamonds in colors of blue, yellow, red and pink occur only in one in every 100,000 diamonds.
Rare and highly valuable diamonds in colors of blue, yellow, red and pink occur only in one in every 100,000 diamonds.
©NMNH/National Gem Collection/2007 Smithsonian Institution

How are Gemstones Formed?

Gemstones are formed in several specific and different ways. Their colors are almost always a result of their chemical composition while they form.

Turquoise

Turquoise forms when water moves through a rock containing copper, aluminum, and phosphorus. Turquoise often occurs in arid or desertenvironments, such as the Southwestern part of the United States. You may be familiar with beautiful Native American jewelry from the Southwest, which is often made with turquoise.

Lapis lazuli

Lapis lazuli is a rock and not a mineral. The turtle sculpture was carved from the semi-precious stone.
Lapis lazuli is a rock and not a mineral. The turtle sculpture was carved from the semi-precious stone.
©Mike Smail
Lapis lazuli forms when magmaunder the surface of the earth forces its way into an existing rock. The magma is so hot that the existing rock melts and then solidifies. This process creates a new deep blue rock, lapis lazuli, which contains the minerals lazurite, pyrite, and calcite.

Garnet

People commonly think of garnets as being red, but they are found in many colors ranging from yellow to black
People commonly think of garnets as being red, but they are found in many colors ranging from yellow to black. Color-changing garnets look different when viewed in daylight and incandescent light.
©NMNH/National Gem Collection/2007 Smithsonian Institution
Garnets often form in hotmetamorphic rocks under great pressure. Garnets occur in every color. Their color is determined by the chemical composition of the melted mineral mix as it solidifies. Red garnets, or pyrope, get their color from magnesium silicate, the melted chemical mixture in which they form.

Jade

Jade was a highly-valued material used in burial ceremonies, royal crowns, jewelry and for the hieroglyphics of many cultures such as the Olmecs of Mesoamerica and Chinese.
Jade was a highly-valued material used in burial ceremonies, royal crowns, jewelry and for the hieroglyphics of many cultures such as the Olmecs of Mesoamerica and Chinese.
©Khanh Vuong
Jade is a gem that can be cut and polished from two minerals: jadeite and nephrite. Both minerals form in metamorphic rocks at high temperature and under high pressure deep within the earth.

Synthetic Gemstones and Gems

Gemstones and gems can be made in laboratories. Scientists try to create the same conditions in the laboratory as in the earth because similar conditions give the gemstones and gems similar properties. Turquoise, sapphires, and rubies can be created in a syntheticenvironment. In one method for making rubies, a rod with a “seed crystal” is lowered into melted minerals and then brought back up. Repeating this process over and over grows a large crystal on the end of a rod from the melted minerals. The ruby can then be detached and cut and polished.

Gemology

Gemology is the study of gemstones, which includes gem properties, locations, and origins. Gemology is often studied by people in the jewelry business, including business owners, buyers, designers, and appraisers. Others studying gemology include antique dealers and auction house catalogers. People in these jobs need to be able to identify gems and gemstones and describe their properties.

Gemstone Classification

Scientists and gemologists have developed a number of ways to classify gemstones: precious or semiprecious, natural or synthetic, and organic or inorganic.
The precious gem, Hope Diamond has been around for centuries and has had many owners during its lifetime. The different owners have re-cut, polished and reset it multiple times, helping shape what it is today.
The precious gem, Hope Diamond has been around for centuries and has had many owners during its lifetime. The different owners have re-cut, polished and reset it multiple times, helping shape what it is today.
©NMNH/National Gem Collection/2007 Smithsonian Institution

Precious or Semiprecious?

This classification is based on beauty, rarity, and hardness. It applies mainly to gems, rather than gemstones. The most beautiful, rarest, and hardest gems are considered precious gems. Precious gems include diamonds, rubies, sapphires, emeralds, aquamarine, topaz, and opals. A semiprecious gem is a gem that is less beautiful, less rare, and less hard. It is also less than 8 on the Mohs’ Hardness Scale, which means it is easier to scratch. Turquoise, jade, lapis lazuli, and amber are all semiprecious.
Would you consider topaz more beautiful than turquoise? It’s hard to say. Classifying gems as precious or semiprecious is fading in popularity because it is easy to disagree about beauty.
A sapphire miner holds several, tiny gemstones in her hand that she collected from the mine in Ankarana Reserve, Madagascar.
A sapphire miner holds several, tiny gemstones in her hand that she collected from the mine in Ankarana Reserve, Madagascar. Many animals such as lemurs, geckos and parrots live in the reserve.
©F.Lanting/Minden Pictures

Natural or Synthetic?

A natural gemstone is one that is formed in the earth. A synthetic gemstone is made in the laboratory. Some gemstones are both. Emeralds, garnets, rubies, sapphires, and diamonds can be both mined from the ground or made in a laboratory.
Have you ever seen a piece of amber with an insect or plant in it? This photo shows the early stages of how amber forms and how easily an ant can get stuck in the sticky tree sap.
Have you ever seen a piece of amber with an insect or plant in it? This photo shows the early stages of how amber forms and how easily an ant can get stuck in the sticky tree sap.
©M.Moffett/Foto Natura/Minden Pictures

Organic or Inorganic?

An organic gemstone is one that is created by a living thing. Pearls are created by oysters and mussels. Amber is sap created by a tree. Coral is created by tiny communities ofanimals in the ocean. Pearls, amber, and coral are organic gemstones. Inorganic gems include diamonds, sapphires, and rubies. These are created by minerals without the help of organisms.

Pearls in Culture

Hundreds of years ago, along the east coast of the United States, Native Americans collected pearls to use in jewelry. Both men and women wore pearl jewelry, including ear pendants with pearls. Pocahontas’ father, Powhattan, reportedly had a collection of pearls given to him as a tribute.

Turquoise in Culture

Turquoise was mined in Persia for thousands of years. It was transported to other places, including Egypt, where it was used by the pharaohs. Much later, turquoise was discovered in the southwestern United States. Now the United States is the largest producer of turquoise.
Quartz is the second most common mineral in Earth's crust. There are many varieties of quartz including rose quartz, smoky quartz and amethyst.
Quartz is the second most common mineral in Earth's crust. There are many varieties of quartz including rose quartz, smoky quartz and amethyst.
©Yiannis Papadimitriou

Quartz in Culture

Quartz is made of silicon and oxygen. Quartz is abundant on Earth and very hard. Because of these properties, it has been used for jewelry for at least 4,000 years. Before quartz was used for jewelry, it was used for spear points. Some people believe quartz can be used for healing.

Opals in Culture

Ancient Greeks believed that opals gave the owner the power to see into the future. Romans believed that these gemstones were a symbol of purity. Arabs believed that opals fell from heaven. However, by the nineteenth century, many people believed that opals were associated with bad luck and should not be worn. Some people today still believe this. But, many others wear opals because they believe they are beautiful.

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