Learning how to identify rocks is the first step in building a collection. Minerals and gemstones have distinct colours, textures, and patterns that distinguish them from the more common, less desirable stones that populate most specimen collection sites. With the right tools, any beginner can learn the tricks of the trade.
- Skill level:
Things you need
- Field guides, geologic maps, rock collecting magazines
- Geologist's hammer
- Hardness kit
- Hand lens
Search natural cliffs, outcrops, quarries, hills, and steep slopes, which offer the best collecting sites, according to the U.S. Geological Survey. You're less likely to find gemstones in level country and open fields.
Review field guides, geologic maps, and rock collecting magazines to learn the make-up of rocks and gems. Understanding that crystals are metamorphic rocks created by the rearrangement of mineral components under additional heat and pressure, for example, will prove critical in developing your identification skills.
Tap the specimen with a geologist's hammer. If the specimen is easily shaped by bending, crushing, or hammering, it is more likely a metallic ore. Gemstones have a crystalline structure that cannot be shaped as easily. Even then, shaping occurs only through abrasion, cutting, or fracturing.
Catalogue each specimen's location in your notebook as you collect it. To avoid errors, save identification tasks for another time, and store each piece in a central container, such as a shoebox.
Run your fingers over the specimen to determine its texture. If the specimen feels rough and sandy, it should never be considered a gemstone, no matter how appealing it looks.
Find Good Specimens
Measure your stone's durability by applying several test substances from a hardness kit. If the first application scratches the specimen, it is probably harder than the stone itself. Try several substances to determine hardness as measured on a Mohs scale, which ranks talc lowest and diamonds highest.
If you suspect a crystalline gemstone, strike your specimen to see how well it breaks. Crystals have a tendency to break along fixed planes, which can be examined and compared to various cleavage charts.
Scratch the specimen against a hard ceramic plate. If the result leaves a streak, the odds of it being a gemstone are higher. To narrow the possibilities, compare the streak's appearance against maps or charts.
Use hand lenses, also called pocket magnifiers, to help identify mineral grains. A six- to ten-power range is best. For best results, use an optically corrected hand lens, which is more expensive but is also considered a more accurate measurement device.
Study the specimen's atomic and molecular structure under a powerful glass to determine if the piece is a crystal. Although sugar and salt crystals may look similar in a bowl, in reality their shapes are unique.
Test the Stones
Tips and warnings
- Expect to build an initial collection slowly. As you meet other collectors, you'll eventually be able to replace lesser pieces through sales or swaps.
- Color is not a reliable indicator of true gemstones. For example, without careful visual examination, telling diamonds apart from their far less rare cousin, cubic zirconia, is difficult.
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