Obsidian
Obsidian (Volcanic Glass)
igneous
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Obsidian
Volcanic Glass (Amorphous Silica)
igneous
Amber
Resinite (Succinite if from the Baltic); Chemical Formula: C10H16O (approximate)
Organic Diamond/Gemstone (often associated with Sedimentary sequences)
Quartzite
Quartzite (SiO2)
metamorphic
River Siltstone Pebble
Siltstone (primarily composed of silica and clay minerals)
sedimentary
Quartzite (River Stone)
Metamorphosed Quartz Sandstone (SiO2)
metamorphic
Apache Tear
Obsidian (Hydrated Volcanic Glass) - SiO2 (with impurities)
igneous
Obsidian
Volcanic Glass (SiO2)
igneous
Quartzite
Metamorphosed Sandstone (Mainly SiO2)
metamorphic
Snowflake Obsidian
Volcanic glass containing Cristobalite (SiO2)
igneous
Obsidian
Volcanic Glass (Primary composition: SiO2 - Silicon Dioxide)
igneous
Quartzite Beach Pebble
Quartzite (primarily SiO2)
metamorphic
Quartzite
Quartzite (SiO₂)
metamorphic
Blue Slag Glass
Ferro-silicate glass (Slag)
igneous (man-made/industrial)
Quartzite Pebble
Quartzite (primarily SiO2)
metamorphic
Obsidian
Volcanic Glass (Amorphous SiO2)
igneous
Quartzite
Quartzite (primarily SiO2)
metamorphic
Precious Opal
Hydrated Silica (SiO2·nH2O)
mineral
Quartzite
Quartzite (mostly SiO2)
metamorphic
Quartzite
Quartzite (primarily SiO2)
metamorphic
Quartzite (River Siltstone variety)
Quartzite (SiO2)
metamorphic
Quartzite with Iron Inclusions
Quartzite (primarily SiO2 with Fe2O3 impurities)
metamorphic
Quartzite Pebble
Quartzite (mostly SiO2)
metamorphic
Pink Opal (Common Opal)
Amorphous Hydrated Silica (SiO2·nH2O)
mineral
Quartzite
Quartzite
metamorphic
Quartzite
Quartzite (consisting primarily of SiO2)
metamorphic
Coquina
Biogenic Limestone (mostly Calcium Carbonate, CaCO3)
sedimentary
Quartzite
Metamorphosed Quartz Sandstone
metamorphic
Quartzite Pebbles
Quartzite (SiO2)
metamorphic
Quartzite
Quartzite (primarily SiO2)
metamorphic
Quartzite Pebble
Quartzite (SiO2)
metamorphic
Black Obsidian
Obsidian (Volcanic Glass, SiO2+)
igneous
Black Obsidian
Amorphous volcanic glass (SiO2 + impurities)
igneous
Obsidian
Obsidian (Volcanic Glass)
igneous
Quartzite pebble
Quartzite (primarily SiO2)
metamorphic
Quartzite Cobble
Metamorphosed Quartz Sandstone (SiO2)
metamorphic
Quartzite River Stone
Quartzite (SiO2)
metamorphic
Siltstone
Siltstone (primarily SiO2 with Al2O3)
sedimentary
Blue Slag Glass
Amorphous Silica (Byproduct of smelting)
Antropogenic (Man-made)
Tektite
Indochinite (Tektite)
igneous
Quartzite Pebble
Quartzite (primarily SiO2)
metamorphic
Black Obsidian
Obsidian (Volcanic Glass, ~70% SiO2)
igneous