Industrial Byproduct (Anthropogenic Rock)

Concrete Rubble with Aggregate

Hardened Portland Cement Paste with Coarse Aggregate

South Korean 100 Won Coin (Cupronickel)

Cupronickel Alloy (75% Cu, 25% Ni)

Queen Conch Shell (Biogenic Calcium Carbonate)

Aliger gigas (synonym Strombus gigas); Composition: Aragonite (CaCO3)

Coal

Carbonaceous sedimentary rock / Lignite to Bituminous coal

Smooth river pebble (exact rock type indeterminate)

Unidentified rounded lithic clast; composition cannot be determined from the photograph

Coal

Combustible Sedimentary Rock

Clear quartz (rock crystal)

Quartz, SiO₂; trigonal crystal system

Smooth gray pebbles

Unidentified rounded rock fragments; composition cannot be determined from the image

Small rounded pebble, likely quartz-rich river or beach stone

Unidentified lithic pebble; exact rock type cannot be determined from the image

Yellow Quartz Pebble

Silicon Dioxide (SiO2)

Mixed beach-stone and tumbled-glass collection

Predominantly uncertain rocks (likely basalt, granite, and quartz-bearing stones) with anthropogenic glass; one possible banded agate or jasper

Red Sandstone

Clastic Sandstone (typically Quartz-rich with Iron Oxide)

Rounded river pebble, likely quartz-rich stone

Unidentified lithic clast; exact mineralogy cannot be determined from the image

Obsidian Arrowhead

Volcanic Glass (Primary composition: SiO2)

Chalcedony

Silicon Dioxide (SiO2)

Rounded brown pebble (rock type undetermined)

Unidentified, iron-stained lithic pebble; composition cannot be determined from the photograph

Shale

Laminated Mudstone (Shale)

Concretion

Sedimentary Concretion

Vesicular Basalt (Lava Rock)

Vesicular Basalt

Quartzite

Quartzite

Man-made Jewelry (Metal and Glass/Plastic)

Synthetic Alloy and Amorphous Solid (SiO2/Polymer)

Goldfish Cracker (Culinary Mimic)

Cibus aurum (Commonly composed of Enriched Wheat Flour and Cheddar Cheese)

Agate

Silicon Dioxide (Chalcedony), SiO2

Small rounded stone, likely a pebble

Unidentified fine-grained lithic pebble; image alone does not support a reliable mineral or rock-species identification

Coal

Bituminous Coal / Carbonaceous Rock

Weathered geode or vug-bearing rock

Likely a quartz- or calcite-lined geode/vug in a host rock; exact minerals cannot be confirmed from the image

Bituminous Coal

Coal (Sedimentary Rock)

Bituminous Coal

Carbonaceous sedimentary rock

Coal

Combustible sedimentary rock

Basalt

Basalt

Opalite-style glass pendant

Man-made opalescent glass (not natural opal)

Orange glassy slag (industrial by-product)

Iron-rich silicate glass; composition varies, commonly Fe–Ca–Al silicate

The user-provided image does not contain a rock or mineral specimen

Rounded gray river pebble, likely basalt or andesite

Fine-grained mafic volcanic rock; commonly basalt (plagioclase, pyroxene, and possible olivine)

Coal

Bituminous Coal

Conglomerate

Clastic conglomerate (rounded pebble- to cobble-sized clasts in a finer matrix)

Small red-brown mineral or rock fragment

Unidentified; possibly iron-oxide-rich jasper, garnet, or weathered sulfide

Digital Multimeter (Synthetic Object)

Digital Multimeter (DMM)

Basalt with Weathering Rind

Basalt (Mafic Volcanic Rock)

Agate

Silicon dioxide (chalcedony, SiO2)

Quartz Vein in Host Rock

Silicon Dioxide (SiO2)

Mixed rock fragments, likely iron-stained quartz-rich material

Indeterminate mixture; visible pale fragments may be quartz or feldspar, with iron-oxide staining (goethite/limonite)