Mineraloid (Human Made Geological Specimen)

Chalcedony (Agate/Chert variety)

Silicon Dioxide (SiO2)

Likely weathered iron-rich rock or slag fragment

Indeterminate; possibly limonite/goethite-bearing rock (FeO(OH)·nH₂O) or industrial iron slag

Fulgurite

Liesegang (Fulgurite)

Tumbled quartz-rich pebble

Microcrystalline quartz (SiO₂), possibly milky quartz or quartzite

Tumbled quartz pebble, possibly citrine or iron-stained quartz

Quartz (SiO₂), likely microcrystalline or granular quartz

Polished black stone, likely basalt or fine-grained mafic rock

Basalt (probable; identification uncertain from photograph)

Polished orbicular gabbro (likely “leopard-skin” or larvikite-type material)

Gabbro, a coarse-grained mafic plutonic rock; chiefly plagioclase feldspar and pyroxene, with possible olivine/amphibole and iron oxides

Opalite (likely man-made glass)

Opalite; amorphous silica glass, not a natural mineral

Chert (Flint)

Microcrystalline Quartz (SiO2)

Tumbled quartz-rich stone (likely milky quartz/quartzite)

Quartz (SiO₂), possibly quartzite with minor iron-oxide staining

Chert (Arrowhead Preform or Point)

Chert (Microcrystalline Quartz, SiO2)

Obsidian

Volcanic glass (SiO2 - Silicon Dioxide with impurities)

Flint (or Chert)

Cryptocrystalline Quartz (SiO2)

Obsidian

Amorphous volcanic glass (SiO2)

Possible iron-rich chert or flint fragment

Microcrystalline quartz (SiO₂), likely hematite/goethite-bearing

Concrete-embedded rock fragment, likely weathered granite or gneiss

Probable granitic silicate assemblage: quartz, feldspar, and dark mica/amphibole

Small clear crystal, possibly quartz or glass-like gemstone

Uncertain; likely quartz (SiO₂), but the image is insufficient to exclude man-made glass or cubic zirconia

White Precious Opal

Hydrated Silica (SiO2·nH2O)

Opalite

Synthetic Glass, SiO2 base with metallic inclusions

Quartz heart (likely milky/included quartz)

Quartz, silicon dioxide (SiO₂)

Tumbled milky quartz

Quartz (silicon dioxide, SiO₂)

Polished silver sheen obsidian heart

Obsidian (volcanic glass), primarily rhyolitic silica-rich glass

Amber (Copal)

Succiniferous Resin

Black Obsidian

Volcanic Glass (predominantly SiO2)

Tumbled milky quartz pebble

Quartz (silicon dioxide, SiO₂)

Polished white calcite (likely satin spar variety)

Calcite, calcium carbonate (CaCO₃)

Tumbled purple quartz, possibly amethyst

Quartz (SiO₂), likely pale amethyst or lavender quartz

Tumbled rose quartz (probable)

Quartz, silicon dioxide (SiO₂), pink variety

Tumbled chalcedony (likely pale agate or quartz pebble)

Microcrystalline silica, SiO₂ (chalcedony; possibly quartz-rich agate)

Tumbled quartz-rich stone, possibly quartzite

Quartzite (mostly SiO₂), visually similar to chert or weathered quartz sandstone

Quartzite

Metamorphic Quartzite (SiO2)

Snowflake Obsidian

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

Possible weathered iron-rich rock or slag fragment

Indeterminate; likely limonite/goethite-bearing material, possibly iron slag

Chert (Green Chert or Jasper)

Microcrystalline Quartz (SiO2)

Tumbled milky quartz (likely quartzite or chalcedony)

Quartz, SiO₂; possibly microcrystalline chalcedony

Tumbled yellow jasper

Microcrystalline quartz (chalcedony), SiO₂, colored by iron oxides

Glass Nugget (Tumbled Glass)

Amorphous Silicon Dioxide (SiO2) with additives

Green aventurine (likely)

Quartzite dominated by quartz (SiO₂), colored by fuchsite mica or other chromium-bearing inclusions

Boulder Opal

Hydrated Silica (SiO2·nH2O)

Tumbled milky quartz (likely)

Quartz, silicon dioxide (SiO₂)

Flint / Chert

Microcrystalline Quartz (SiO2)

Chert (Flint)

Microcrystalline quartz (SiO2)