Rockhounds and Rocks

Malachite, a forest green semi-precious gemstone marbled with pale green streaks, usually takes the form of a globular mass although it sometimes occurs as a spray of porcupine quill-like projections. Strikingly beautiful and easily workable, malachite has found a place in the craft of jewelry making since prehistoric times in some parts of the world.  It forms when copper interacts with carbonated water or limestone.  It occurs commonly in the copper mines of Arizona and southwestern New Mexico. 

Volcanic bombs, which blast like cannonballs out of a crater vent during an eruption, sometimes form as a glob of magma encapsulating a cluster of olivine crystals, with a few rich enough in color and quality to be rated as the gemstones called peridots.  The olivine crystals, translucent to transparent, range in color from green to yellowish green to white or brown.  They have a high melting temperature.  The best peridots, which have a bright green color, found places as settings in the jewelry of Egyptian royals.  Volcanic bombs with olivine crystals and peridots have been found in Kilbourne Hole and one other volcanic crater in south-central New Mexico. 

Fossils – the mineralized remains or the impressions of plants or animals – offer a whole new dimension to rock collecting, namely, a record of the emergence and development of life in changing environments on earth through hundreds of millions of years.  Fossils almost always occur in sedimentary rocks.  “The process of fossilization [of plant or animal remains],” says the Enchanted Learning Internet site, “involves the dissolving and replacement of the original minerals in the object with other minerals”  Impressions of, for instance, plant leaves or animal tracks left in sediment, will be preserved if the sediment turns into rock before the impression erodes away.  Fossils commonly occur in limestone deposits.  Fossil treasure troves occur in every state in the Southwest. 

Meteorites don’t speak to the history of the earth, of course, but they do tell us something of the early history of our solar system, bringing yet another dimension to collecting rocks.  Broadly classified as stony, stony iron or iron, meteorites may represent debris left over from the formation of the solar system or material blasted into space by surface collisions on other solar system bodies, for instance, the moon or Mars.  Typically, meteorites disintegrate as they heat up from friction when entering the earth’s atmospheres, 50 to 70 miles above the surface, and the fragments fall to earth in a scatter across what is called a “strewn field.”  One meteorite strewn field lies in Arizona’s Mojave County, where the University of Arizona has worked to recover and analyze fragments and map the impact area. 

Where Do I Look for Rocks and Minerals?

You will discover interesting rocks in numerous places across the desert Southwest, many of them mentioned in DesertUSA articles.  You will find James R. Mitchell’s gem trail series of books to be especially useful guides to rewarding locations.  For instance, Mitchell provides text, maps and photographs for more than 80 proven sites in his Gem Trails of Southern California.  He provides comparable information and directions in his gem trail books on Nevada, Arizona, Utah, New Mexico and Texas.  (You can acquire his books through DesertUSA’s Trading Post,   Chris Pellant’s Rocks and Minerals, a descriptive reference with clearly written text and excellent photographs, will serve as a useful field guide for collectors. 

What Equipment Do I Need?

In the field, you will need a geologist’s rock hammer, chisels, a good knife (for testing sample hardness), a hand lens (for examining crystals and grain), cloth and plastic sample containers, a topographical map, a compass, and a note pad (for documenting your finds).  Importantly, you should come equipped with safety equipment, especially safety goggles, a hard hat and heavy work gloves.  An injured eye, fractured skull or shredded hands can spoil your whole day.  At home, you will need scrapers, brushes and, preferably, distilled water for cleaning samples. 

How Do I Identify Rocks and Minerals?

Often, with a reference such as Pellant’s Rocks and Minerals, you can identify a rock or mineral by a simple examination of physical characteristics such as color, hardness, luster, cleavage, crystalline form, specific gravity and magnetism.  For instance, olivine, from volcanic bombs, has a color that is greenish, a hardness that is greater than a steel nail, a luster that is dark and nonmetallic, and cleavage that is jagged.  For another rock or mineral, you may have to determine the density (weight for a given volume) or the magnetism to aid in the identification.  You may have to submit others to chemical or fluorescent light tests. 

Often, one of the most definitive characteristics of a rock or a mineral is its hardness, which you can determine by comparing it against the standardized Mohs Scale of Hardness:

Your fingernail has a hardness of about 2.5, so it would leave a scratch on a gypsum stone.  Glass has a hardness of about 6 to 7, so it would scratch the rocks and minerals with a hardness of 1 through 5.  A copper penny has a hardness of about 3, a knife blade, of about 5.5.  You can buy a test kit of hardness-testing tools with points calibrated to the Mohs scale. 

Can I Collect Rocks Legally on Public Lands?

Typically, you may be allowed to take “reasonable” amounts of rocks, minerals, invertebrate fossils and petrified wood in non-restricted areas, without using power equipment, for your personal collection, but because regulations vary with the location and the administrative state or federal agency, you should check with the proper local officials before you begin collecting. 

Meeting Other Rock Hounds

If you would like to get acquainted with other rock hounds, you will likely find an association, society or club nearby.  Visit the United States Club List, produced and maintained by rockhound Albert Zabinski.  Here you will find an “online list of over 900 U.S. Gem, Mineral, Lapidary, Fossil, and just about anything to do with rocks clubs, guilds, associations, and societies”

Rock Hound Mecca

Every January and February, hundreds of thousands of snow birding and RVing rock hounds make a pilgrimage to Arizona, especially to Quartzite and Tucson, to renew old friendships, gossip, compare notes, tell yarns, swap rocks and minerals, and buy and sell specimens.  In Quartzite, in western Arizona, they shop at eight major shows, where 2000 vendors sell rocks, minerals, gems, fossils and handcrafts in one of the world’s largest outdoor flea markets.  In Tucson, at the annual gem and jewelry show – the largest in the world – they can visit nearly 40 different venues during late January and early February.  They can, as the Whirled Planet Internet site says, “find everything from fossils and mineral specimens to beads to high end diamond jewelry.  If it’s made from stone, chances are [they] can find it in Tucson.”

Rocks and Kids

Families often discover that scouring the countryside for rocks can be as much fun as panning streams for gold.  It often yields more immediate rewards.  Moreover, kids may discover that a rock can have a purpose almost as exciting and satisfying as serving as a missile for smashing a window or smacking a cousin’s head.  In fact, youngsters may come back from a trip telling stories about the stories that rocks tell. 

By Jay Sharp

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Rockhounding Places To Go
Hunting Desert Meteorite Treasures
Desert Rocks, Minerals & Geology Index
Desert Survival Primer
Rock and Stuff in DesertUSA Store