Green obsidian is a subject of much confusion and debate among geologists and consumers alike. Obsidian is a naturally occurring volcanic glass formed when lava cools too quickly for crystals to form, resulting in an amorphous structure. While the existence of naturally occurring green volcanic glass is confirmed, the vast majority of bright green material found for sale is manufactured. The disparity between the extremely rare natural form and the common man-made glass drives the current market confusion.
The Formation of Obsidian and Typical Coloration
Obsidian forms from felsic, silica-rich lava that cools with great speed, which prevents the organization of atoms into a crystalline structure. This rapid cooling defines the material as a natural glass with a smooth, vitreous luster.
The typical dark color of obsidian, usually jet-black or dark brown, is due to trace amounts of impurities, commonly microscopic inclusions of iron oxides such as magnetite or hematite. While pure obsidian would be colorless, the presence of these transition elements almost always results in a dark appearance. Other colors like red or mahogany obsidian are also attributed to varying levels of iron content.
Certain varieties of obsidian display unique optical effects, like the golden sheen in Sheen Obsidian or the rainbow effect in Fire Obsidian. These phenomena are caused by thin-film interference from trapped gas bubbles or nanoinclusions of minerals like magnetite, not by the body color of the glass.
Natural vs. Manufactured Green Obsidian
Natural green obsidian is an extremely scarce material, sometimes appearing as an iridescent blue or green flash within a darker stone, known as Sheen Obsidian. True green body color is occasionally reported from specific geological sites, where the coloration is often a subtle, slightly greenish-gray tint. This rare natural hue is only noticeable when light passes through a thin section and is linked to microscopic crystals of minerals like feldspar or varying amounts of iron and magnesium.
This rarity contrasts sharply with the overwhelming supply of bright green “obsidian” on the market, which is almost always human-made glass. These simulants are often sold under misleading trade names like “green obsidian” or “Volcanic Glass,” sometimes falsely linked to locations like Mount St. Helens. Manufactured products include slag glass, a waste byproduct of iron-smelting, or melted bottle glass dyed a vibrant color.
These artificial glasses are designed to mimic the appearance of a rare stone, often exhibiting colors like transparent blue, red, or vibrant emerald green that do not occur in nature. Genuine green volcanic glass, where it exists, is typically much darker, often semi-opaque, and lacks the uniform saturation of the fakes.
Consumer Guide to Identifying Authenticity
Transparency and color saturation are immediate identifiers of a fake. Manufactured green glass is typically uniform, highly transparent, and brightly saturated, whereas natural obsidian is usually opaque or only slightly translucent at the thin edges.
The presence and shape of air bubbles provide another strong clue. While natural obsidian can contain microscopic gas bubbles, manufactured glass and slag often feature large, perfectly spherical air bubbles visible to the naked eye. Natural obsidian bubbles, such as those in Sheen Obsidian, are often stretched into flattened or torpedo shapes aligned with the rock’s flow.
The way the material breaks, known as the fracture, is a key characteristic. Natural obsidian exhibits a conchoidal fracture, creating curved, shell-like surfaces and extremely sharp edges due to its amorphous structure. Experts can distinguish natural stone by the presence of flow lines or tiny mineral inclusions, which are absent in pure man-made glass. Consumers should also be wary of extremely low prices or unverified sources, as genuine natural material is exceedingly rare and commands a premium.