Hecatolite

Hecatolite is a form of feldspar, a mineral that forms from volcanic magma. It is known more commonly as Moonstone.

Real World Properties
The most common variety is white with a slight bluish tint.

It got its common name for its ability to diffract light within its layers.

This shimmering quality is also why Hecatolite was first used by many ancient civilizations as jewelry.

The Romans romanticized the mineral and its properties as "solidified moonlight". Some on the sub-continent of India still consider the stone to be sacred.

In astrology it is associated with the Moon and is the birthstone for those born in June.

Fictional Properties
Hecatolite is used as a fictional construct within the world of MTV's Teen Wolf and can have serious physical effects on werewolves.

Observed Effects on Werewolves
The mineral can apparently scatter moonlight and block the effects of the full moon on werewolves.

This has the effect of stopping their transformations and lowering their tolerance to the effects of the full moon.

Once exposed to moonlight again, the werewolves lose all control under its influence.

Example

 * Boyd and Derek's younger sister, Cora, were locked in a bank vault made largely of Hecatolite laced stone. This kept them from shifting for three full moons diminishing their tolerance to it. Once the walls of the vault were breached and the light of the full moon reached them they lost all control and tried to kill their friends and family members. (see Chaos Rising)