Frequently Asked Questions - General

FAQs - General

A rock hound collects rock and minerals. A lapidary cuts and polishes rock and mineral specimens. Rock hounds may or may not work the material they collect. Lapidaries may or may not spend time in the field collecting specimens. Typically each does a little of both.

No! We at CCR (Cooke City Rocks) are lapidaries only. Our material comes from private land, estate sales, other lapidaries or rock hounds, and rock shows. While there may be nothing like the thrill of the find, the constraints of time (we are in Cooke for the entire summer) and special restrictions applicable to commercial use of collected material, and the ready availability of collected material have moved us to be processors only.

We are often asked this question. Achieving a high-quality polish begins with obtaining a nice cut on the rock. This requires using a quality diamond blade. Cheaper blades usually, but not always, give inferior results. A cheap blade may plow through the rock, but often the resulting surface is too rough to practically polish.

Fig.1 - A specimen being cut on one of our 24"saws.

After cutting, the specimen is placed in a tub of kitty litter or automotive oil absorber overnight to soak up the cutting oil. The rock is then "stabilized", which merely means any cracks are filled with cyanoacrylate adhesive. This serves two purposes; it helps prevent fracture of the specimen during subsequent sanding and polishing operations, and prevents polishing compound from accumulating in fissures or pockets in the rock.

Fig.2 - Our 36" Rotating Flat Lap.

The next step involves removal of the saw marks. This is accomplished by using a 36" rotating flat lap. This happens to be a custom-fabricated machine, but commercially available lapidary equipment exists to do this. The advantages of this machine are its speed and potential to grind 4-20 pieces simultaneously. Rocks are ground in a water/silicon carbide slurry. The process takes 30 minutes to two hours. The rocks are then hand-sanded. The machine is a dry sander that uses silicon carbide belts. Four different grit belts are used- 100, 220, 400, and 600. Fig. 3 is a picture of the "Bull Wheel". This machine is fast. I begin sanding with the long axis of the specimen, and rotate 90 degrees at each belt change.

Fig.3 - A Bull Wheel.

The final step is polishing. We use another machine we had fabricated for us- a 36" rotating lap dedicated to polishing. There are numerous lapidary polishing compounds on the market. Again, this machine is fast- a specimen can be final polished on the machine in as little as thirty minutes.

Fig.4 - Our Polisher.

We maintain a good selection of tumbled stones. Achieving a polish is a time-consuming process involving increasingly fine tumbling grits. We use both rotary and vibratory tumblers. A typical sequence takes about a month. We always encourage those interested in beginning rock tumbling to purchase quality equipment. There can be quite a “learning curve” in obtaining nicely polished stones, and cheaper equipment only makes the learning process more difficult.

Fig.4 - Some of our 40 pound rotary units.

We are often asked how trees turn to stone. When you pick up a piece of petrified wood you are looking at the result of several processes that have occurred over extremely long periods of time. The first requirement is that the wood be covered somewhat rapidly with material that excludes oxygen. This is termed an anaerobic or anoxic condition. This is necessary to prevent natural decomposition. This rapid covering may be a mud flow, ash or other pyroclastic event. This rapid entombing means petrified wood is often found in areas of past volcanic activity. Yellowstone has a long history of volcanic activity, and it is reported as many as twenty seven layers of petrified wood exist in the park, the result of many centuries of volcanic activity.

Fig.5 - XXXXXX.

The second step requires the presence of water. Typically surface water percolates through the overlying material (such as volcanic ash) and reaches the encased wood. A process called permineralization occurs in which the mineral-laden ground water fills pores in the wood and gradually replaces all organic matter. Sometimes this results in a very accurate three dimensional copy of the original wood structure.

Finally, uplift and/or erosion occurs to expose the petrified piece. From this process, it is easy to understand that only a small percentage of living trees are ever petrified- the vast majority decay. Of those buried, not all are exposed to the requisite water, and of these only a fraction are eventually exposed for the collector to find.

Sometimes "limb casts" are found. These may resemble the shape of the original wood, but no visible wood structure remains. The original limb may have been reduced to ash, or may have decomposed leaving a hollow cavity in the rock that is subsequently filled or partially filled with minerals. Gradations between limb casts and preserved specimens exist. Blue Forest wood from Wyoming frequently has combinations of cell structure and agate pockets visible.

Fig.6 - XXXXXX.

Petrified wood is a fossil. Different terms, some used inaccurately, are encountered when discussing petrified wood. Some are synonyms for the process, and others refer to more specific minerals deposited in the process. Thus terms as silification, fossilization, agatized wood, opalization, and pyritization are used.

Fig.7 - XXXXXX.

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