A crystal habit. Needle-like.

A brilliant luster with high reflectivity. Adamantine luster is extremely shiny. Hard minerals and lead bearing minerals typically have adamantine luster.

A term usually applied to rocks with small hollow or partially filled voids. If filled with a mineral, these are nodules (solid) or small geodes typically composed of zeolite or silica.

A crystal that has no faces.

A crystal habit. Flat and long, like a knife or Wrigley gum stick.

A crystal habit. Blocky or equi-dimensional, brick-shaped.

A crystal habit. In aggregate, forms grape-like groups.

A mineral characteristic describing its tenacity. A brittle mineral is easily broken into many pieces with a slight blow of a hammer.

A crystal habit. Hair-like. Filiform.

A non-determinative but indicative mineral property. The appearance of a mineral's surface which reflects a band of light which appears to move as the sample is rocked back and forth. These wavy [..]