When you think of Quartz gemstones, what comes to mind? Is it the icy sparkle of Crystal Quartz? Or the delicate pink of Rose Quartz? Did you know that this diverse group of gemstones also includes Amethyst, Tiger's Eye, Citrine, Aventurine, Smoky Quartz and Chalcedony? The stones classified as Chalcedony also represent a diverse group. They include Agate, Fire Agate, Chrysoprase, Jasper, Onyx, Carnelian and Bloodstone. The first of these, Agate is a beautiful and varied classification of stones.

Agates are formed inside cavities of volcanic rock where either volcanic gas created pockets in the lava, or where limbs of trees or other organic matter decomposed. Unlike Rock Crystal which has a large crystalline structure, micro crystals of agate are formed inside these volcanic pockets by silica-rich water washing into the cavity. Over time, layers of chalcedony and quartz are formed, creating concentric bands of agate. Many agates are found with hollow interiors because the layers of agate simply have not filled the entire space. In these cases, there are often crystals of amethyst, smoky quartz or crystal quartz in the agate hollow. These sugar-like crystals are known as "Drusy" and are often used in jewelry unpolished to highlight their sparkly nature.

Some agates, such as Blue Lace Agate, Banded Agate and Botswana Agate have rings or scallops of color. Others, like Tree Agate and Moss Agate have delicate fern or tree-like patterns that are created from the presence of iron ore in the crystals. There is also Mexican Agate, which has "eyes" rather than bands of color.

Agate can be purchased in many forms. Egg-shaped geodes with agate and drusy centers are often cut as bookends and other objects, or carved into decorative bowls. Agate bowls were popular collector's items in Renaissance Europe, and the Louvre has a large collection of them. Slices of Agate make beautiful pendants, coasters or even panes in stained-glass windows. Agate is also the traditional stone for cameos, with many agates having color ranges from white to black with all shades of brown in between, allowing for detailed carvings. Since Agate is a hard stone, it can be cut and faceted into all sorts of shapes for beads. Round striped agates evoke glass marbles and larger slab-shaped beads showcase the intricate patterns or translucent layers of stone.

Sources:
www.gemstone.org
http://wikipedia.org
Gems and Precious Stones, edited by Kennie Lyman, ©1986 Simon & Schuster
Smithsonian Handbooks Gemstones, by Cally Hall, ©2002 DK

Quartz Family Chalcedony Family Agate Bloodstone Carnelian Chalcedony Chrysoprase Fire Agate Jasper Onyx / Sard / Sardonyx