Organic (Geological Interest)

Quartz (Grain)

Silicon Dioxide (SiO2)

Pyritic Sandstone

Clastic Sedimentary Rock (Pyrite-bearing Sandstone)

Quartz (Iron-Stained)

Silicon Dioxide (SiO2)

Quartz / Common Quartzite

Silicon Dioxide (SiO2)

Sandstone with Quartz Vein

Arenite with hydrothermal quartz intrusion

Siltstone

Siltstone (composed of microscopic quartz and clay minerals)

Granite featuring Quartz Vein

Granite with hydrothermal silica (SiO2) intrusion

Milky Quartz

Quartz (Silicon Dioxide, SiO2)

Peridotite

Ultramafic igneous rock (primarily olivine and pyroxene)

Small dark mineral/rock fragment

Indeterminate; possibly magnetite-bearing basalt or iron-rich slag

Quartz pebble or seed/crumb

SiO2 (if quartz)

Milky Quartz

Quartz (Silicon Dioxide, SiO2)

Ironstone Concretion

Siderite or Hematite-bonded Concretion

Ironstone Concretion

Siderite or Hematite Concretion

Fluorite-Gedrite in Quartz (Schist)

Fluorite (CaF2) with Gedrite in Quartz/Feldspar Matrix

Weathered iron-rich basalt or laterite

Basalt, likely limonitized/goethite-stained; exact identification requires testing

Possible weathered metal-rich rock or slag fragment

Uncertain; possibly iron-oxide-rich breccia or industrial slag

Likely iron-rich rock or metallic mineral fragment

Uncertain; possibly limonite/goethite-rich material or weathered iron meteorite fragment

Rounded river pebble

Indeterminate; likely quartz-rich sandstone, chert, or weathered volcanic rock

Schist with Quartz/Mica

Mica Schist (primarily Muscovite and Quartz)

Epidote

Epidote (formula: Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH))

Weathered quartz-rich metamorphic rock, likely quartzite

Quartzite (mostly microcrystalline SiO₂), possibly iron-stained mica-bearing quartzite

Quartz (Iron-stained Pebble)

Silicon Dioxide (SiO2)

Milk Quartz (or Milky Quartz)

Silicon Dioxide (SiO2)

Ironstone Nodules / Siderite Concretion

Siderite (FeCO3) / Ferruginous Septarian Concretion

Quartz Vein in Mica Schist

Quartz (SiO2) with Muscovite/Biotite Schist

Sandstone (Ferruginous)

Arenite with iron oxide cement (Fe2O3)

Red Coral

Corallium rubrum (Calcium Carbonate, CaCO3 with Carotenoid pigments)

Possible weathered iron-rich rock or slag fragment

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

Reddish-brown crystalline rock, possibly weathered granite or garnet-bearing schist

Indeterminate; likely quartz–feldspar–mica rock with iron oxides, potentially garnet-bearing

Soil with Mineral Detritus and Quartz Fragments

Regolith / Silicate Mineral Aggregate

Horse Chestnut (Buckeye seed)

Aesculus hippocastanum seed

Yellow Quartzite

Quartzite (primarily SiO2)

Weathered sandstone fragment

Quartz-rich sandstone, likely feldspathic or lithic sandstone

Shale with Limonite/Hematite Staining

Argillaceous sedimentary rock with Iron Oxides (FeO(OH)·nH2O / Fe2O3)

Iron Ore / Hematite Rock

Iron oxide (primarily Hematite, Fe2O3)

Weathered quartz-rich pebble

Milky quartz, chiefly silicon dioxide (SiO₂), possibly with iron-oxide staining and minor feldspar

Black Pearl (Tahitian Pearl)

Aragonite / Calcite (CaCO3) with Conchiolin

Limonite-stained Quartz

Silicon Dioxide (SiO2) with Hydrated Iron Oxide (FeO(OH)·nH2O) coatings

Weathered iron-rich concretion (probable limonite/goethite)

Limonite–goethite aggregate, approximately FeO(OH)·nH₂O

Chert Nodule

Chert (SiO2)

Basalt with Quartz/Feldspar Vein

Amygdaloidal Basalt with Plutonic intrusion (SiO2/KAlSi3O8)