Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock.

It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high viscosity and polymerization degree of the lava. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Obsidian is hard and brittle; it therefore fractures with very sharp edges, which had been used in the past in cutting and piercing tools, and are still used as surgical scalpel blades.

Pliny's Natural History features volcanic glass called "Obsidianus", so named from its resemblance to a stone found in Ethiopia by one Obsius.

Obsidian is mineral-like, but not a true mineral because as a glass it is not crystalline; in addition, its composition is too complex to comprise a single mineral. It is sometimes classified as a mineraloid. Though obsidian is usually dark in color similar to mafic rocks such as basalt, obsidian's composition is extremely felsic. Obsidian consists mainly of SiO₂ (silicon dioxide), usually 70% or more. Crystalline rocks with obsidian's composition include granite and rhyolite. Because obsidian is metastable at the Earth's surface (over time the glass becomes fine-grained mineral crystals), no obsidian has been found that is older than Cretaceous age. This breakdown of obsidian is accelerated by the presence of water. Obsidian has low water content when fresh, typically less than 1% water by weight, but becomes progressively hydrated when exposed to groundwater, forming perlite. Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis.

Jan Johnston (born 21 February 1968, Salford, Lancashire, England) is an English professional singer, best known for collaborating with some of the world's top trance music DJs.

In the early 1990s she was signed to Columbia Records as part of the pop duo JJ, which gained some recognition while touring the UK.

However, when the band project failed she continued as a solo artist; signing to A&M Records. In the mid 1990s she came to the attention of trance producer, Brian Transeau, when he purchased one of her singles from a bargain bin in Manchester. Impressed by her vocals, he decided to collaborate with her recording the track "Remember."

Following this, Johnston was in demand to vocal for many other trance tracks, notably for Alan Bremmer and Anthony Pappa's "Freefall" project. Upon being given the instrumental, Jan came up with the lyrics resulting in "Skydive (I Feel Wonderful)" which despite being a club anthem, never translated to a commercial hit, finally hitting the top 40 at #35 on its third release in 2001. Paul Oakenfold signed her to his Perfecto Records label in 1999 to record an album. The resulting album 'Emerging' was delayed numerous times, with her first Perfecto release being a track she recorded with BT years earlier entitled "Flesh", rather than an actual track from the album, which reached #36 in the charts. The original version of "Flesh" has never been released, only remixes. A cover of The Carpenters' song, "Superstar", was lined up to be the album's first single, with remixes produced by Todd Terry and Bill Hammel, but would ultimately go on to be unreleased. Only one track from 'Emerging' was released as a single; "Silent Words" in 2001, with the album ultimately being unreleased.