Gemstone color

Color is the most obvious and attractive feature of gemstones. The color of any material is due to the nature of light itself. Daylight, often called white light, is actually a mixture of different colors of light. When light passes through a material, some of the light may be absorbed, while the rest passes through. The part that is not absorbed reaches the eye as white light minus the absorbed colors. A ruby appears red because it absorbs all the other colors of white light - blue, yellow, green, etc. - except red.

The same material can exhibit different colors. For example ruby and sapphire have the same chemical composition (both are corundum) but exhibit different colors. Even the same gemstone can occur in many different colors: sapphires show different shades of blue and pink and "fancy sapphires" exhibit a whole range of other colors from yellow to orange-pink, the latter called "Padparadscha sapphire".

This difference in color is based on the atomic structure of the stone. Although the different stones formally have the same chemical composition, they are not exactly the same. Every now and then an atom is replaced by a completely different atom (and this could be as few as one in a million atoms). These so called impurities are sufficient to absorb certain colors and leave the other colors unaffected.

As an example: beryl, which is colorless in its pure mineral form, becomes emerald with chromium impurities. If you add manganese instead of chromium, beryl becomes pink morganite. With iron, it becomes aquamarine.

Some gemstone treatments make use of the fact that these impurities can be "manipulated", thus changing the color of the gem.

Herkimer Diamonds

"Herkimer Diamonds" is the name given to the doubly terminated quartz crystals found in Herkimer County, New York and surrounding areas. Examples of these crystals are shown in the photo at right. Note that these crystals have the typical hexagonal habit of quartz, however, instead of having a termination on one end they are doubly terminated. This is a result of the crystals growing with very little or no contact with their host rock. Such doubly terminated crystals are very rare and this is part of what makes Herkimer Diamonds so popular with mineral collectors.

The host rock for Herkimer Diamonds is the Cambrian-age, Little Falls Dolostone. The Little Falls Dolostone was deposited about 500 million years ago and the Herkimer Diamonds formed in cavities within the dolostone. These cavities are frequently lined with drusy quartz crystals and often are coated with a tarry hydrocarbon (see image below).

Although Herkimer County, New York is the location for which these crystals are named, similar doubly terminated quartz crystals have been found in a few other locations, including Arizona, Afghanistan, Norway, Ukraine and China. They have the same appearance but can not rightfully be called "Herkimers". The doubly terminated quartz crystals shown in the lower right photo are from a deposit in Afghanistan

A Gem Among Diamond Mines

Arkansas, The Natural State, is blessed with an abundance of geological wonders. Crater of Diamonds State Park, the only diamond-producing site in the world open to the public, stands
out as a unique geological "gem" for you to explore and enjoy.Here, you are invited to prospect in the park's diamond search area, a 37-acre plowed field that is the eroded surface of an ancient volcanic pipe that 95 million years ago, brought to the surface the diamonds and some of the semi-precious stones lucky visitors find here today.

Diamonds of all colors of the rainbow can be found here at Crater of Diamonds, but the three most common colors unearthed by park visitors are white, brown and yellow. Crater of diamonds State Park is a rockhound's delight since, along with diamonds, more than 40 types
of rocks and minerals can found here, too. These rocks and minerals include lamproite,
amethyst, banded agate, jasper, peridot, garnet, quartz, calcite, barite and hematite.

In 1906, John Huddleston, the local farmer who owned this property then, found the first diamonds near Murfreesboro, Arkansas, and started the diamond mining rush. According to the
history of Crater of Diamonds State Park, after a series of ill-fated diamond mining
ventures, followed by tourist attractions, the diamond mine site became an Arkansas state
park in 1972.

Within the park boundary, many remnants of old mining ventures remain, including the Mine
Shaft Building, the Guard House, mining plant foundations, old mining equipment and smaller
artifacts. Nowhere else is North American diamond mining history as evident or as well reserved as here.Along with the diamond search area, the park has hundreds of acres of natural forest featuring a diversity of flora and fauna and offering visitors interesting things to do.

Arkansas's natural and cultural diversity -- the geology, history, plants and animals --

makes Crater of Diamonds State Park a unique Arkansas attraction unlike any other in the world. You are invited to visit this one-of-a-kind attraction and experience the thrill of
digging for diamonds in the rough. Our park staff will identify your finds for you. And unlike other diamond mines, our park has a policy of "finders keepers." Any diamonds,semi-precious stones, rocks or minerals you unearth are yours to keep, regardless of their value.