Quartz is one the most abundant minerals on earth and can be found in many shapes, sizes and colors. Many experienced rock collectors can tell if a crystal is real quartz through careful examination. They examine the crystal for small naturally accruing abnormalities (man-made crystals are usually flawless, without abnormalities). Natural quartz crystals will have areas with small cracks, cloudiness or areas where other minerals are forming. Because of the natural flaws, a grade system was developed to determine the quality of the crystal. Grade A quartz is the highest quality of quartz. This grade is identified by its crystal clear transparence, and lack of abnormalities within the crystal's structure. Grade B quartz contains a small amount of natural abnormalities with a small number of tiny cracks in the crystal, and may have small cloudy areas. Grade C quartz will have small chips along the edges, slight damage to the point and several small cracks that do not damage the crystal's structure. Grade D quartz has damaged points and large cracks that damage structure of the crystal, making it very fragile and easily broken. A simple method to determine if a crystal is real quartz is to a perform a scratch test using the Mohs scale of hardness as a guide. The Mohs scale, developed in 1812 by German mineralogist Friedrich Mohs, is a popular guide used to measure the hardness of gemstones by judging scratch resistance. Quartz has a hardness of 7 on the Mohs scale, meaning that it will easily scratch glass, metals and softer stones. This test will not harm the crystal if it is real quartz because glass has a hardness of 5.5 to 6.5.
Clean the surface of the glass, with a streak-free glass cleaner. Completely dry the surface with paper towels.
Examine the glass for scratches. Mark scratches using a permanent marker.
Press the point of the crystal firmly against the surface of the glass. Add a small amount of pressure as you drag the crystal across the surface.
Examine the surface of the glass carefully; the scratch will be faintly visible. If no scratch is visible, repeat the test adding more pressure as you drag the crystal.
If after several tests the surface of the glass is unaffected, you may want to consider trying to scratch the crystal. Find an unscratched, flat area of the crystal and repeat step 1.
Press the corner of the glass firmly against the surface of the crystal. Add a small amount of pressure as you drag the glass across the surface.
Examine the surface of the crystal. If a scratch is visible on the surface, the crystal it is not real quartz.
Performing this test on artificial crystal will damage the surface and destroy the value. Be careful when applying pressure to the point of a crystal. Sharp points may break off during testing if too much pressure is applied.