SiO₂

These samples of gwendel quartz are displayed in the Smithsonian Museum of Natural History. Gwendel is a variety of quartz , which has the composition SiO₂. The sample at left is about 20 cm across and is from Tiefengletscher, Furka, Uri, Switzerland.

This sample is also from Uri, Switzerland. It is about 6 x 12 cm.

Gwendel (sometimes spelled gwindel) implies twisted quartz crystals. They are almost always smoky in color, and are prized by collectors.