Obsidian has earned the popular name of "volcanic glass" for it's resemblance to glass. It has similarities to the appearance of glass because of a high silica content that is between 60% and 85%. Obsidian is classified as a rock. and occurs when silica rich ejected magma rapidly cools. This specimen originated from New Zealand. The conchoidal fracture is the result of rapid cooling prohibiting the development of a crystal structure which would have cleavage planes. This type of amorphous material is known as a mineraloid. With the passage of time the unstable obsidian can begin to crystallize and radial clusters of cristobalite can form at random in the obsidian, thus creating the attractive "snowflake obsidian. The word cochoidal is derived from the description of a shell " conch", semicircular.