Mineralogical

Limonite (Iron Ore Congcretion)

Limonite (a mixture of hydrated iron(III) oxide-hydroxides, FeO(OH)·nH2O)

Polished black obsidian

Volcanic glass; primarily silica-rich rhyolitic glass (approximately 70–80% SiO₂)

Polished black obsidian

Volcanic glass; primarily silica-rich rhyolitic composition (approximately 70–80% SiO₂)

Black obsidian

Volcanic glass; predominantly rhyolitic silica-rich melt (approximately 70–80% SiO₂), lacking crystalline structure

Obsidian (likely snowflake-free black variety)

Volcanic glass; primarily SiO₂-rich rhyolitic composition

Mahogany Obsidian

Volcanic Glass with Hematite/Magnetite inclusions

Black Obsidian

Obsidian (Volcanic Glass, ~70% SiO2)

Obsidian

Volcanic Glass (SiO2)

Snowflake Obsidian (Flower Jasper variant)

Vitreous volcanic silicate with cristobalite inclusions

Mahogany Obsidian

Volcanic Glass (Silicate: SiO2 + Fe2O3)

Opal

Hydrated Amorphous Silica (SiO2·nH2O)

Obsidian

Volcanic Glass (SiO2 rich)

Limonite (with Pyrite)

Limonite (Hydrated Iron Oxide) - FeO(OH)·nH2O

Limonite (Ironstone Concretion)

Limonite (Hydrated iron(III) oxide-hydroxide, mixtures of FeO(OH)·nH2O)

Obsidian (likely black volcanic glass)

Obsidian; predominantly silica-rich rhyolitic volcanic glass (approximately 70– on 80% SiO₂)

Polished black obsidian

Volcanic glass, predominantly rhyolitic silica (SiO₂)

Likely obsidian fragment

Volcanic glass, predominantly silica-rich rhyolitic composition (SiO₂-rich)

Obsidian (likely Apache tear or flaked obsidian)

Volcanic glass; primarily rhyolitic silica glass (SiO₂-rich, non-crystalline)

Mahogany Obsidian

Obsidian (Volcanic Glass with Hematite inclusions)

Gold Sheen Obsidian

Volcanic Glass (SiO2 + impurities)

Mahogany Obsidian

Volcanic glass (SiO2 with Hematite/Magnetite inclusions)

Polished mahogany obsidian (likely)

Volcanic glass; primarily silica-rich rhyolitic glass (SiO₂), with iron oxides

Polished black obsidian pyramid/block

Obsidian — natural volcanic glass, chiefly rhyolitic silica (approximately 70–75% SiO₂)

Snowflake Obsidian

Volcanic Glass with Spherulite Inclusions (primarily SiO2)

Black Obsidian

Obsidian (Volcanic Glass)

Snowflake Obsidian

Volcanic Glass with Spherulite Inclusions (70–75% SiO2)

Limonitic Iron Ore / Goethite

Hydrated Iron(III) oxide-hydroxide (primarily FeO(OH)·nH2O)

Obsidian

Obsidian (Volcanic Glass), primarily SiO2 (Silicon Dioxide)

Obsidian

Obsidian (Volcanic Glass, SiO2)

Limonite (Iron Ore)

Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)·nH2O)

Mahogany Obsidian

Volcanic Glass (predominantly SiO2 with inclusions of Hematite or Magnetite)

Mahogany Obsidian

Volcanic glass (SiO2 with Hematite or Magnetite inclusions)

Limonite (Iron Ore)

FeO(OH)·nH2O (Hydrated iron(III) oxide-hydroxide)

Snowflake Obsidian

Volcanic glass with Cristobalite inclusions (mostly SiO2)

Tektite (likely Australite)

Tektite (no specific chemical formula as it's a natural glass of variable composition, mostly SiO2, Al2O3, FeO, MgO, CaO, K2O, Na2O, TiO2)

Mahogany Obsidian

Volcanic glass (Silicon Dioxide with Hematite/Magnetite inclusions)

Obsidian (likely black volcanic glass)

Obsidian; primarily amorphous volcanic silica glass, approximately SiO₂-rich rhyolitic composition

Obsidian

Obsidian (Volcanic Glass)

Snowflake Obsidian

Spherulitic Volcanic Glass (SiO2 + impurities)

Obsidian

Volcanic Glass (Silica / SiO2)

Limonite Concretion

Hydrated iron(III) oxide-hydroxide (FeO(OH)·nH2O)

Obsidian

Volcanic Glass (predominantly SiO2)