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? 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. 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 gravity, hardness,
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.
| Mineral |
Hardness |
| Talc |
1 |
| Gypsum |
2 |
| Calcite |
3 |
| Fluorite |
4 |
| Apatite |
5 |
| Feldspar |
6 |
| Quartz |
7 |
| Topaz |
8 |
| Sapphire |
9 |
| Diamond |
10 |
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.
©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 desert environments,
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.
©Mike Smail Lapis lazuli forms when magma under
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. Color-changing garnets look different
when viewed in daylight and incandescent light.
©NMNH/National Gem Collection/2007 Smithsonian Institution Garnets often form in hot metamorphic
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.
©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 synthetic environment. 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.
©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. 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.
©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 of animals 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.
©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.