Animium (aa-nim-ee-um)

Animium, or as it is more commonly referred to as Soul Stone, is an incredibly rare mineral that is formed deep within the earth. Like most precious gems, it is formed under extreme heat and pressure, but also requires intense magical energy in order to develop its distinguishing property: the ability to house the essence of a living creature. This ability could be compared to saving data on a memory chip. A refined piece of soul stone could be made to contain a person's soul while their body continues to exist in the material world, or could hold the information of the creature's physical body along with its essence, allowing for the body to be reconstructed when the soul is released.
This property makes soul stone the base component of life-containing magic items like phylacteries, iron flasks, and mirrors of life trapping. Fortunately, it's scarcity and unique circumstances required for its formation means that these dangerous objects are few and far between.

Properties

Material Characteristics

While the color of soul stone varies depending on where it is found and how it is formed, it can be recognized by distinctive, lightning-like streaks found throughout the material; mementos of the raw magic needed to form it. 
Generally, soul stone is either red, purple, or blue in hue. On rare occasions it can be colorless.

Type

Ore/Mineral

Color

Semi-opaque gemstone (color varies depending on formative circumstances)

Common State

crystalline gemstone