Sunday, April 5, 2009

How to make rocks beautiful

Rocks that Rock
Originally published in April 4, 2009 in the Santa Cruz Sentinel

I was recently seduced by a rock. This was no ordinary rock mind you—it was poppy jasper, a miraculous combination of ringed, blood-orange blossoms against a vibrant gold background. It can be found only one place in the world—Morgan Hill, California—about 15 miles east of Santa Cruz, as the crow flies. This stone had been shaped into an oval—a double-sided cabochon in lapidary lingo—with a surface as shiny as glass by my new friend, rockhound Carla Fairey.

It haunted me over the next few weeks, and I finally decided I had to have it (and that’s saying a lot for someone who didn’t even want a wedding ring when she got married). When I called Carla, she invited me over to see her workshop. And I got not only an exquisite $75 pendant, but a mini-lesson in geology. I was fascinated by her breadth of knowledge about rocks, including mineral composition and geologic history. But she also has a lot of practical knowledge such as how to recognize “a keeper,” even when, to my eye, it looks like a ragged chunk of concrete.

What is a Rock?

Basically, rockhounds are looking for any material—rock, mineral, shell, fossil, petrified wood, volcanic glass, whale bone—that’s beautiful, durable and rare. Rocks are generally a combination of minerals and organic matter. Granite, for instance, is made up of quartz, feldspar, mica, and sometimes tourmaline, epidote, and more. Rocks may contain tiny microscopic grains of minerals or organic substances, or coarse agglomerates of different minerals, where the individual minerals are easily discernible. The kinds of rocks that attract lapidarians are ones with good color, exceptional pattern, translucency or other special optical qualities. A skilled lapidarian can cut and polish a stone to enhance these qualities.

Cuttability is also a factor. Each mineral is assigned a hardness on the Mohs scale, which rates talc as 1 and diamond as 10. Minerals that are too soft do not hold a polish well. Minerals that are harder, will take much longer to polish than a softer material. And those in the 8 ½ to 9 range may to too difficult to polish with standard equipment.

Where do you find rocks?

Carla and her husband, Rusty, have searched out rocks all over the western U.S. and even down into Baja, Mexico. Each state or region has its own unique collection of rocks. “The harder it is to get, the more it’s worth it,” says Carla. But some collectors prefer to finding rocks closer to home. Although California deserts are often the richest mineral sources, desirable rocks can be found locally along beaches, and in creeks and quarries. Mike Humenik, a long-time member of the Santa Cruz Mineral and Gem Society says he doesn’t go hiking with his wife any more because “we can’t go more than 12 feet without her poking around.”

Some collectors specialize in a certain kind or even size of rocks. For instance, Mike has recently started collecting microscopic minerals, which he mounts on tiny pedestals in one-inch square black boxes. He hands you a magnifying loop so that you can actually see these tiny specimens. Carla’s favorites are ones that make eye-catching pendants, such as poppy jasper, fossil rocks, banded onyx and blue shattuckite.
Popular guidebooks to help you get started include Rockhounding California and Gem Trails. Members of the Santa Cruz Mineral and Gem Society (SCMGS) ( are also willing to point you in the right direction. They have monthly meetings, occasional field trips, and make their lapidary workshop available on Saturday mornings for a small fee. (Also see Mike Humenik’s great article on Local Rockhounding—where to go and how to do it legally--at

How do you make a rock shiny?

Once you’ve found, traded for, or purchased a rock with possibilities, you have to work to get it to that brilliant, polished state. Rocks can be polished by tumbling or by cutting and grinding.
Tumbling involves placing rocks of like hardness and size into a rubber-lined barrel (a rotary tumbler) with abrasive grit and water. The barrel is then placed on slowly rotating rails so that, like rocks in a stream bed, they get smoother and smoother as they tumble over each other. The basic procedure is to tumble the rocks with progressively finer grits and polishes until the desired shape and shine is achieved. It may take 4 to 6 weeks to finish a batch. (See for one rockhound’s tumbling recipes and timetables.)

If you want a rock with a specific shape for jewelry—a cabochon (“bald head” in French)—you don’t need to tumble it. A large rock may first need to be cut into wedges with a slab saw. Then, those wedges can be cut down to size and surplus removed with a trim saw. All lapidary equipment—saws and grinding wheels—is specially designed for cutting rocks, with a constant infusion of water to keep things cool. “If the rock gets too hot, it will fracture,” says Carla. “The water also helps keep the dust particles down.”

The cut stone is then shaped further on a succession of grinding and polishing wheels, to create the highly polished, domed top. (A flat rock cannot be made nearly as shiny as a convex one.) Depending on the hardness of the stone, the grinding and polishing can take anywhere from ½ hour to several hours. (See for one rockhound’s step-by-step process, including safety precautions.)

How do you get started?

Every rockhound has their own particular collecting style—whether they find or buy their rocks, and what they choose to do with them. Much of what they know comes from trial and error, after years of working with rocks. Fel di Geronimo, 92, another SCMGS member, says he’s been collecting and grinding stones since he was 12 years old. But these days he’s just happy to pass on what he’s learned over 80 years of collecting on Saturday mornings with Mike at the SCMGS lapidary shop. He’ll also be sitting near the entrance at the upcoming SCMGS Annual Show, Saturday & Sunday, April 25-26, from 10 am - 5 pm at the Santa Cruz Civic Auditorium—identifying rocks, answering questions, giving free rocks to kids, and introducing neophytes to the seductive powers of rocks.