How to Identify Valuable Rocks
- 1). Look for an imperfect stone that you suspect might be a diamond. Diamonds are naturally flawed, whereas cubic zirconia, their best imitator, is optically flawless. If the stone looks too perfect, be suspicious. Use Archimedes’ method: fill a small graduated cylinder with a little bit of water (1 to 2 mL for a 10-mL cylinder), record the original volume, drop the stone in and record the change in volume. Dry off the stone and determine its mass on a balance or small gram scale. Use this information to find the density; diamond has a density of 3.51 g/mm; cubic zirconia has a density of 5.5 to 5.9 g/mm.
- 2). Check for air bubbles and smaller crystals that could be rubies or sapphires (corundum). Synthetic corundum is usually splintered from aluminum oxide powder. Since powder does not always melt uniformly, there are bound to be some unusual flaws. Curved growth and color lines are also a giveaway. Scratch a sharp angle of the stone against glass such as an empty beverage bottle. Do not press too hard; it’s not necessary, and the bottle may break if you do. If the glass is scratched, chances are the stone in question is corundum. Glass has a hardness of 7 on the Moh scale, whereas corundum rates at a 9. Also, use the density test from Step 1. Corundum has a density of around 4 g/mm, whereas topaz, which is also valuable, is about 3.5 g/mm.
- 3). Inspect the label on the topaz or quartz rock if you are buying it in a store. Topaz should be labeled as topaz with only two typical flourishes--“precious” and “imperial.” All other names designations, including “oriental,” “smoky” and “Madeira” are not for real topazes. Scratch a sharp angle of the rock against a glass bottle. Citrine, or yellow quartz, is the most common imitator and will not scratch glass because they are chemically identical. The other common imitator is “oriental topaz,” or yellow corundum.
- 4). Scratch quartz at a sharp angle against a glass bottle. Quartz will not scratch glass, since both are composed of silicon dioxide. Natural, uncut quartz ideally grows out in hexagonal prisms. If by some awful calamity you drop something that you think is quartz, see if it breaks into smaller hexagonal parts parallel to the length of the original piece. This tells you it is quartz.
- 5). Bite a pearl gently. If it has a gritty feel, it is a real pearl. If you are not sure of your jaw strength, rub two pearls together. They will feel grainy against each other. Also, look at the holes drilled in the bead. If it is smooth without rising up or falling in about the aperture, then it is probably real.
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