Smoky quartz

Smoky Quartz, also known as cairngorm or moorland topaz, was a variety of quartz that was often found in massive deposits. The black variety of this stone was called morion and was used in necromancy.

Description
Smoky quartz ranged in color from brownish-yellow to brown to black and was usually brilliant cut into faceted gems regularly used to decorate weapons. Morion was used in magical inks and as a necromantic spell component. A typical specimen had a base value of 50 gp.

Powers
When bones were immersed in a solution that included morion they became hard as steel and immune to hostile necromantic effects. For example, a magic item made with morion-treated bone could not be affected by a rival necromancer who attempted to disrupt its magical function by targeting the bone material.