Sedimentary (Microcrystalline Silicate)

Chalcedony

Silicon Dioxide (SiO2)

Polished gray marble slab

Calcite-rich marble (recrystallized limestone; chiefly CaCO₃)

Common Opal (Potch)

Hydrated Silica (SiO2·nH2O)

Quartz–feldspar–mica metamorphic rock, likely gneiss

Gneiss; composition commonly quartz (SiO₂), feldspars, biotite/hornblende, and minor accessory minerals

Weathered iron-rich limestone or altered volcanic rock

Probable limonite/goethite-bearing calcite rock; exact identification requires testing

Tumbled Agate

Silicon Dioxide (SiO2)

Rhodonite

Manganese Silicate (Mn,Fe,Mg,Ca)SiO3

Milky Quartz or Moonstone

Silicon Dioxide (SiO2) or Potassium Aluminum Silicate (KAlSi3O8)

Jasper

Microcrystalline Quartz (SiO2)

Weathered iron-rich rock, possibly garnet schist or mica schist

Foliated metamorphic rock; likely mica schist with iron oxides and quartz, but exact identification is uncertain from the image

Anthracite Coal

Anthracite (Carbon-rich metamorphic rock)

Weathered limestone

Calcite-rich limestone (primarily CaCO₃)

Brecciated jasper, possibly rainforest jasper or brecciated rhyolite

Brecciated microcrystalline quartz (SiO₂), commonly called jasper; the green portions may contain epidote, chlorite, or iron-bearing silicates, while red-brown areas are typically hematite or other iron oxides

Plume Agate

Silicon Dioxide (SiO2) - Chalcedony Variety

Tumbled Mixed Gemstones and Rocks

Various mineral species including quartz (SiO2) and silicate minerals

Chert / Quartzite

Silicon Dioxide (SiO2)

Chert / Flint Arrowheads

Cryptocrystalline Quartz (SiO2)

Shiva Lingam

Cryptocrystalline Quartz (Jasperiod Silicate with Iron Oxide inclusions)

Sea Glass

Man-made silicate glass (Amorphous silicon dioxide)

Rounded gray pebble

Indeterminate; likely a water-worn silicate or carbonate pebble

Quartz-veined Metamorphic Pebble

Silicate-rich metamorphic rock with quartz veins (SiO2)

Likely sandstone or weathered quartz-rich rock fragment

Quartz-rich sandstone; exact identification is uncertain from the photograph

Almandine Garnet

Iron aluminum silicate (Fe3Al2(SiO4)3)

Jasper

Microcrystalline quartz (SiO2)

Tumbled river stones (likely quartzite, jasper, and chert)

Varied silicate rocks, chiefly quartzite (SiO₂), jasper/chert (microcrystalline SiO₂)

Green-and-white quartz-rich rock, likely chrysoprase or serpentine-bearing stone

Uncertain; possible chrysoprase (microcrystalline quartz, SiO₂) or serpentinite (magnesium silicate minerals)

Ironstone Pebble

Iron-rich Sedimentary Rock (Fe2O3 / FeO(OH))

Chert (Flint / Jasper)

Silicon Dioxide (SiO2)

Rhodonite

Manganese Silicate (Mn,Fe,Mg,Ca)SiO3

Red Jasper

Silicon Dioxide (SiO2) with Iron Oxide inclusions

Marble

Recrystallized Carbonate Rock (CaCO3)

Polished Nephrite Jade

Calcium magnesium iron silicate hydroxide - Ca2(Mg,Fe)5Si8O22(OH)2

Polished gray pebble, likely quartzite or chert

Quartzite (mostly SiO₂), tentative identification

Chert (Common Opal/Chalcedony variety)

Microcrystalline Quartz (SiO2)

Weathered iron-rich rock, likely hematite–goethite-bearing basalt or ironstone

Basalt/ironstone matrix with hematite (Fe₂O₃), goethite [FeO(OH)], and possibly limonite

Blue Quartz (Aventurine)

Silicon Dioxide (SiO2) with Crocidolite or Magnesio-riebeckite inclusions

Mixed river gravel, prominently iron-stained chert/jasper

Microcrystalline quartz (SiO₂), chiefly chert/jasper with iron-oxide staining; mixed clasts may include quartzite and other silicates

Mixed rock and mineral collection

Multiple specimens; visible pieces may include quartz, calcite, agate/chalcedony, jasper, and dyed or coated materials

Sandstone (Ferruginous)

Arenite with Iron-Oxide Cement

Banded Chert / Cryptocrystalline Quartz

Silicon Dioxide (SiO2)

Chert (Jasper variation)

Silicon Dioxide (SiO2)

Rounded gray pebble

Indeterminate; likely fine-grained quartz-rich silicate rock