Sedimentary (Chemically Precipitated)

Dolomite on Prehnite (Saddle-shaped Dolomite)

Dolomite [CaMg(CO3)2] on Prehnite [Ca2Al(AlSi3O10)(OH)2]

Blue apatite (likely dyed or enhanced)

Apatite group; fluorapatite, Ca5(PO4)3F, is the common blue variety

Tiger's Eye

SiO2 (Quartz pseudomorph after crocidolite)

Flint

Microcrystalline quartz (SiO2)

Banded ironstone (likely)

Iron-rich, silica-bearing rock; possibly a fragment of banded iron formation (BIF)

Iron-stained quartz-rich rock (likely ironstone or ferruginous quartz)

Ferruginous quartz-rich rock; exact mineralogy cannot be determined from the photograph

Weathered ironstone concretion (possible hematite/goethite concretion)

Hematite–goethite-rich ferruginous concretion; primarily Fe₂O₃ and FeO(OH) in a silica/clay matrix

Chert on Volcanic Host Rock

Sedimentary Chert (SiO2) within Basalt or Andesite

Moqui Marble (Sandstone Concretion)

Hematite-cemented Sandstone (Fe2O3 + SiO2)

Septarian Nodule

Septarian Concretion (CaCO3 with Siderite/Calcite)

Blue Apatite

Calcium phosphate fluorapatite, Ca5(PO4)3(F,Cl,OH)

Chert / River Jasper

Microcrystalline Quartz (SiO2)

Chalcedony (Agate / Quartz Geode Fragment)

Silicon Dioxide (SiO2)

Mica

Phyllosilicate group (e.g., Biotite or Muscovite)

Chert (Flint Nodules)

Cryptocrystalline Quartz (SiO2)

Moqui Marble (Shaman Stone)

Ironstone Concretion (Goethite/Hematite Shell)

Weathered limestone

Calcite-rich limestone (predominantly CaCO₃)

Sandstone (Ferruginous)

Arenite (Fe-rich SiO2)

Chert Nodule in Limestone (Flint in Chalk)

SiO2 (Microcrystalline Quartz) in CaCO3 (Calcite)

Red Jasper

Microcrystalline Quartz (SiO2)

Honey calcite cluster

Calcite (calcium carbonate, CaCO₃)

Quartz / Common Opal Transition

Silicon Dioxide (SiO2)

Chert / Flint

Microcrystalline Quartz (SiO2)

Banded calcite (likely cave deposit or vein fragment)

Calcite, CaCO₃

White quartz geode nodule

Quartz (SiO₂), likely a quartz-lined geode or vug in a host rock

Iron-rich concretion or weathered ironstone

Goethite–hematite limonite aggregate; commonly described as limonite or ironstone

Red Jasper

Silicon Dioxide (SiO2) with Hematite inclusions

Limestone with Calcite Crystals

Sedimentary Rock containing Calcium Carbonate (CaCO3)

Pebble / Chert

Microcrystalline Quartz (SiO2)

Hematite-rich ironstone concretion

Hematite (Fe₂O₃), likely mixed with goethite/limonite and silica

Honey calcite (orange calcite)

Calcite, calcium carbonate (CaCO₃)

Orange Calcite

Calcium Carbonate (CaCO3)

Iron-rich sandstone (Gozan/Ironstone)

Ferruginous Sandstone (clastic sedimentary rock)

Blue Apatite

Fluorapatite (Ca5(PO4)3(F,Cl,OH))

Fluorite

Calcium Fluoride (CaF2)

Fossiliferous Limestone with Brachiopod

Limestone (Calcium Carbonate, CaCO3) with Phylum Brachiopoda fossil

Iron-rich concretion or weathered ironstone

Goethite–hematite-rich limonite (FeO(OH)·nH₂O / Fe₂O₃)

Weathered iron-rich concretion

Goethite–hematite limonite concretion, likely with quartz and clay minerals

Moqui Marbles

Ironstone Concretions (Hematite / Goethite / Sandstone)

Jasper

Microcrystalline Quartz (SiO2)

Fossiliferous Limestone with Rugose Coral

Calcite (CaCO3) containing a Rugosa (Horn Coral) fossil

Ferruginous Sandstone

Arenite with limonite/goethite cement