Fire Agate
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Tom's Bio | Thousand Oaks | Fire Agate

When he was alive, my father worked with rocks and became a specialist in Fire Agate. I'll describe what Fire Agate is here and how to process it and then show some examples of stones my father worked.

What is Fire Agate?

Fire Agate is a layered stone. The layers are small enough that light entering them forms interference colors known as "fire." The gem is thought to be formed when hot water saturated with colloidal silica and iron oxide invades cavities in country rock and begin to cool. Chalcedony with iron oxide begins to grow on any available surface (the iron oxide gives the basic brown color to the gem). As the solutions began to precipitate and grow layers of silica and iron oxide would be deposited depending on the relative level of those elements in solution and underlying conditions. These alternating silica and iron oxide layers (Schiller layers) cause the brilliant fire in the gem. As iron oxide ran out in the solution colorless chalcedony continued to grow.

Cutting Fire Agate essentially reverses nature's process by grinding and polishing away layers, following natural contours, until only the fire is visible. As you might imagine, however, one layer too far and the stone is ruined.

[Click on pictures of stones on this page in order to display a full 640x480 JPEG file of that stone with attached descriptive information. Better pictures will be exchanged for these and added when I get lighting and technique down and a little time.]

Mounted bolo

Large bolo

Directions for Cutting Fire Agate
(Notes my father left)

Inspect the rough stone by wetting with water under a bright light. Direct light is ideal. (The stone is fragile so hold it over a padded surface.)

Observe the depth and location of color layers. The gem material (fire layers) are usually covered by chalcedony. Trim away excess chalcedony by sawing, grinding, or sanding.

Sawing should be used only for the top portion of chalcedony which has no color. Leave 1/8th inch for grinding.

For grinding, use a 100 grit wheel. Grind for not more than four of five seconds. Stop and examine for signs of fire under bright light. Shape the stone in any direction the fire indicates. Do not overheat the stone.

Remember -- Grind slowly and inspect often!

When you are satisfied that you have exposed all the fire, grind on a 600 grit wheel to eliminate scratches. Then start with 325 diamond paste, moving to 600, then 1200, 3000, and finally 50,000.

Reminder: In all of the above steps of grinding use plenty of water. Do not overheat.

"The Thinker"
Tom's Bio | Thousand Oaks | Fire Agate

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