Quartz (silicone dioxide) is found in abundance around the world, being Earth’s second most common mineral after feldspar. Shape-wise, rock quartz forms crystals in hexagonal prisms with sharp ends of six-sided points looking like little pyramids; however, some quartz embedded in rock has an irregular mass, with no definite shape. Color-wise, while most quartz is colorless and transparent, it does come in a variety of colors as well, including purple, red, brown, pink, black, blue, green, etc.; the color depends on whether it's found in igneous, metamorphic or sedimentary rocks. You can test quartz: Since quartz is extremely hard (quartz has a hardness of 7 on the Mohs scale), it will be very hard to scratch if scraped with a blade, but take care not to injure yourself if you try this test.