GLOSSARY
Amorphous—without [crystalline] structure and therefore without regular form.
Balcones fault zone—a [system] of [faults] extending from north of Waco in McLennan County, through Travis and Bexar counties, to near Del Rio in Val Verde County (see [p. 42]).
Boulder—a large rock or mineral fragment that has a diameter greater than 256 millimeters (about 10 inches).
Breccia—a rock made up of sharp-cornered, cemented fragments with diameters greater than 2 millimeters (about ⁸/₁₀₀ of an inch).
Cambrian—the earliest [period] of the [Paleozoic] [Era] (see [p. 3]).
Cenozoic—the present [era], one of the great divisions of geologic time (see [p. 3]). This era began about 63 million years ago.
Clastic—made up of broken fragments of rocks or minerals.
Cleavage—occurs when minerals split along smooth flat surfaces that are parallel to possible crystal faces. These planes as well as crystal faces are controlled by the crystal lattice or atomic structures of the minerals.
Cleavage fragment—a mineral specimen that has been broken along its planes of [cleavage].