Black Obsidian
Volcanic Glass (Natural Glass) · Semi-Precious Gemstone / Decorative Stone
Crystal System
Amorphous (Non-crystalline)
Mineral Group
Mineraloid
Chemical Formula
SiO2 (Silicon Dioxide with various impurities and water)
Formation Process
Extrusive igneous process formed by the rapid cooling of viscous felsic lava (rich in silica) without sufficient time for crystal growth
About This Crystal
The specimen is a polished, teardrop-shaped tumbled stone of deep, uniform black color. It has a high-gloss vitreous to sub-vitreous luster, reflecting light sharply from its smooth, curved surfaces. It is completely opaque with a sleek, tactile texture typical of tumbled and polished volcanic glass.
Physical Characteristics
Color is jet black with no visible color zoning; streak is white; no cleavage planes; exhibits distinct conchoidal fracture with razor-sharp edges on unpolished pieces; specific gravity is approximately 2.35 to 2.60; tenacity is brittle; non-magnetic; inert under UV light.
Optical Properties
Singly refractive (isotropic) due to its amorphous structure; refractive index is approximately 1.48 to 1.51; exhibits no pleochroism, birefringence, or dispersion in its solid opaque black form.
Hardness & Durability
Origin Region
United States (Oregon, California), Mexico, Iceland, Italy, Japan, and other regions with recent volcanic activity
Hardness & Durability
Mohs hardness is 5 to 5.5, making it moderately hard but susceptible to scratching by harder gemstones like quartz (7). Toughness is low due to its brittle nature and extreme tendency toward conchoidal fracture upon impact.
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic cleaners and steam cleaning which can fracture the stone. Store separately in a soft pouch to prevent scratching from harder minerals.
Rarity & Value
Common; widely available and affordable. Value is determined by size, quality of polish, and absence of surface blemishes. Treatments are rare since the raw material is abundant.
Special Characteristics
Due to its amorphous glassy structure, obsidian breaks with a famous conchoidal fracture that produces edges significantly sharper than high-quality surgical steel. Certain varieties may contain micro-inclusions that create sheen, snowflake patterns, or rainbow effects, though this specific specimen is uniform black.
Lore & History
Historically used by ancient civilizations such as the Aztecs and Mayans to create sharp weapons, arrowheads, mirrors, and ceremonial objects. In modern metaphysical practices, black obsidian is widely regarded as a protective grounding stone believed to absorb negative energy and promote emotional clarity and spiritual introspection.