Quartz Hardness: 7 Streak: White Environment: All environments What to look for: Light-colored and very hard crystals, veins, pockets, or pebbles Size: Quartz can be found in a large range of sizes; as masses larger than a basketball or crystal points smaller than a pea Color: Colorless to white, brown to red, purple Occurrence: Very common Notes: Quartz is the single most abundant mineral on the planet, so every rock collector, amateur or professional, should know both how to identify it and the forms it takes. Quartz consists of silicon and oxygen, otherwise known as silica, which is colorless or white when pure, but it can take on a rainbow of colors depending on impurities. Well-formed quartz crystals, commonly called "rock crystals," are six-sided and are found in cavities within rock. Quartz also commonly fills vesicles (gas bubbles) and cracks within rocks, appearing as pockets or veins. Beach-worn quartz masses are found as translucent white, round pebbles. Quartz is also one of the primary ingredients in rhyolite and granite, which makes those rocks very hard and weather-resistant. The identifying features of quartz are very important to know. Aside from its very high hardness and six-sided crystal points, quartz has a glassy luster and conchoidal fracture, which means that when struck or broken, quartz cracks or breaks in a rounded, half-moon shape. All quartz-based minerals will exhibit this fracture. Finally, quartz will produce a spark when struck with a metal object. Where to Look: Quartz specimens are easily picked up on the Keweenaw's lakeshore and in copper mine dumps. Excerpted from Michigan Rocks and Minerals: A Field Guide to the Great Lake State by Dan R. Lynch, Bob Lynch All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.