Ironstone Concretion (Limonite/Goethite)
Ferruginous Sandstone / Ironstone (FeO(OH)·nH2O)
sedimentary
Category
Industrial Byproduct (Often Mistaken For Obsidian Or Mineral)
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Iron-stained Quartz
Silicon Dioxide (SiO2) with Hematite/Limonite impurities
mineral
Sodalite
Na8(Al6Si6O24)Cl2 (Sodium Aluminum Silicate Chloride)
mineral
Obsidian with Slate/Tuff
Volcanic glass (SiO2) with associated pyroclastic rock
igneous
Black Onyx
Silicon Dioxide (SiO2) with carbon impurities
mineral
Siltstone
Siltstone (composed of clastic quartz and feldspar)
sedimentary
Yellow Quartzite or Yellow Jasper
Quartzite (primarily SiO2 with Iron oxide staining)
metamorphic
Dumortierite Quartz
Dumortierite (Al7BO3(SiO4)3O3) in Quartz (SiO2)
metamorphic
Scoria (Lava Rock)
Vesicular Basalt / Scoria
igneous
Siltstone
Siltstone (primarily SiO2 with Al2O3)
sedimentary
Vesicular Basalt (Scoria)
Vesicular Basalt
igneous
Mahogany Obsidian
Obsidian (Volcanic Glass with Hematite/Magnetite inclusions)
igneous
Obsidian Arrowhead
Volcanic Glass (70% or more SiO2)
Igneous
Quartzite (Iron-stained River Rock)
Metamorphic Rock consisting primarily of Quartz (SiO2)
metamorphic
Apache Tear (Obsidian)
Volcanic glass (SiO2 - Silicon Dioxide)
igneous
Siltstone
Siltstone (primarily SiO2 with Al2O3)
sedimentary
Sandstone (specifically an Iron-Concretion)
Arenite with Iron Oxide (Limonite/Goethite) cementation
sedimentary
Milky Quartz
Quartz (Silicon Dioxide - SiO2)
mineral
Sodalite
Sodalite (Na8(Al6Si6O24)Cl2)
mineral
Silver Sheen Obsidian
Volcanic Glass (SiO2)
igneous
Quartzite
Quartzite (primarily SiO2)
metamorphic
Quartzite
Quartzite (primarily SiO2)
metamorphic
Pyrite (Fool's Gold)
Iron Disulfide (FeS2)
mineral
Serpentine
Serpentinite (group of minerals based on (Mg,Fe,Ni,Al,Zn,Mn)2-3(Si,Al,Fe)2O5(OH)4)
metamorphic
Snowflake Obsidian
Volcanic Glass with Cristobalite Inclusions
igneous
Mixed Tumbled Gemstones (Agate, Aventurine, Pyrite, etc.)
Multiple (principally Silicon Dioxide SiO2 and Iron Disulfide FeS2)
mineral
Green Aventurine
Quartz variety (SiO2 with inclusions)
mineral
Sodalite
Sodalite (Na8(Al6Si6O24)Cl2)
mineral
Snowflake Obsidian
Obsidian with Spherulitic Cristobalite (SiO2)
igneous
Sodalite
Na8(Al6Si6O24)Cl2
mineral
Amazonite
Amazonite (KAlSi3O8); a green variety of Microcline feldspar
mineral
Sodalite
Sodalite (Na8(Al6Si6O24)Cl2)
mineral
Obsidian
Volcanic glass (no mineral formula due to amorphous structure, mostly SiO2)
igneous
Ferruginous Quartz (Iron-stained Quartz)
Silicon Dioxide (SiO2) with iron oxide inclusions/staining (Limonite/Hematite)
Mineral
Lapis Lazuli
Lapis Lazuli (Primary mineral: Lazurite, (Na,Ca)8(AlSiO4)6(S,Cl,SO4,OH)2)
metamorphic
Snowflake Obsidian
Spherulitic Obsidian (primarily SiO2)
igneous
Black Onyx
Silicon Dioxide (SiO2) with cryptocrystalline structure
mineral
Ironstone Concretion
Siderite or Hematite Concretion
sedimentary
Snowflake Obsidian
Vitreous volcanic rock with Cristobalite inclusions (mostly SiO2)
igneous
Blue Quartzite (Blue Aventurine / Dumortierite Quartz)
Quartzite with inclusions (SiO2 with AlAl4BSi3O18)
metamorphic
Black Obsidian
Obsidian (Volcanic Glass, SiO2 + impurities)
igneous
Black Obsidian with white veins
Volcanic Glass (70–75% SiO2)
igneous