19-Quartzite

Metamorphic rock which originated as quartz sand, perhaps on a beach in Canada, 1 to 3 billion years ago. The sand was first buried and lithified to form sandstone, after which it was subjected to high pressures, probably during a mountain-building episode, and converted to quartzite. The quartz grains were recrystallized and pressed together tightly, giving the rock a strong, cohesive character. (Compare with no. 21, no. 23, no. 27, and no. 28.)