Steampunkers USA Big Heart Collection - 20mm Classic Obsidian Black - 20" Adjustable Soft Black Poly Woven Washable Cord Stainless Bail - Natural Crystal Gemstone Carved Necklace Charm Beautifully shaped 0.79" (20x20x4 mm) carved heart, Smooth polished surface, & 20-24" Adjustable black soft satin necklace cord. Strong stainless steel bail. Obsidian is a naturally occurring volcanic glass. It is commonly considered a gemstone despite having no defining crystalline growth/structure. Obsidian is formed when chemically favorable lava flows cool above ground. The Mahogany variety includes bands of reddish hue cause by iron. Snowflake obsidian contains cristobalite inclusions. It is also popular as a healing stone. Gemstones have natural variations, no two are alike. A unique gift for yourself or that special someone! Every gemstone is handpicked and individually inspected for optimum quality by Steampunkers USA.