Obsidian is a naturally occurring volcanic glass formed when lava cools rapidly. Green obsidian, a distinct variety, is considered rare due to its unique color and specific formation conditions. This article explores its characteristics, geological origins, factors influencing its rarity, and how to identify genuine specimens.
Understanding Green Obsidian
Green obsidian is a natural glass distinguished by its green coloration. This hue typically results from trace elements like iron and chromium within the silicon dioxide-rich glass. Microscopic mineral inclusions like chlorite or serpentine can also contribute to the green color. The specific shade of green can range from a pale, translucent green to a deep, mossy green that might appear almost black in certain lighting conditions.
Like all obsidian, it possesses a smooth, glassy texture due to rapid cooling, which prevents large mineral crystal formation. It exhibits a vitreous luster, reflecting light similarly to glass, and fractures with smooth, curved conchoidal surfaces. This volcanic glass has a Mohs hardness of approximately 5 to 5.5, making it moderately durable but susceptible to scratches.
Geological Origins and Global Presence
Obsidian forms from silica-rich felsic lava that cools very quickly upon extrusion from a volcano, resulting in minimal crystal growth. This rapid cooling often occurs when lava comes into contact with air or water, such as during a lava flow or volcanic dome formation. High silica content contributes to the lava’s viscosity, inhibiting atom diffusion and preventing crystallization.
For green obsidian to form, specific geological conditions are necessary, including particular minerals within the volcanic source. Iron and magnesium often impart the green hue to the volcanic glass. Gas bubbles trapped within the lava during crystallization can also enhance the green coloration or create a sheen effect. Natural green obsidian is found in specific regions with a history of volcanic activity. Notable locations include the Hidalgo obsidian mine in Mexico, Glass Buttes in Oregon, USA, and deposits in Brazil, Guatemala, parts of California, and Mayor Island in New Zealand.
Factors Affecting Its Rarity
Green obsidian is relatively rare compared to common varieties like black obsidian. The specific geological conditions required for its formation, including the precise concentration of trace elements like iron and chromium, are less common than those that produce typical dark obsidian. While black obsidian is widespread in volcanically active regions, green obsidian deposits are more localized and less abundant.
The perceived rarity of green obsidian is also influenced by market dynamics and the prevalence of imitations. Its unique color can command higher prices, sometimes leading to the sale of artificially colored glass or other minerals misrepresented as genuine. Mining limitations and sporadic new discoveries further contribute to its limited availability.
Identifying Genuine Green Obsidian
Distinguishing genuine natural green obsidian from imitations requires careful observation of its physical characteristics. Its color can range from pale to deep mossy green, sometimes appearing almost black. Avoid pieces with an overly bright, uniform, or artificial-looking green color, as these may indicate dyeing or artificial treatment.
Genuine green obsidian feels smooth and glassy, not rough or pitted. It often exhibits a vitreous luster and may show a subtle sheen or iridescence from microscopic mineral or gas bubble inclusions. Natural inclusions, flow lines, or small fractures are common imperfections in genuine obsidian and can even enhance its authenticity. Completely flawless green obsidian might suggest an artificial material. It is typically translucent to semi-translucent, allowing some light to pass through.