Basalt

Dark tumbled stone, likely basalt or black chert

Probable basalt (fine-grained plagioclase–pyroxene rock); chert is an alternative

Weathered volcanic rock, likely basaltic scoria

Vesicular basalt/scoria; primarily plagioclase, pyroxene, olivine, and iron oxides

Vesicular basalt (scoriaceous basalt)

Basalt; chiefly plagioclase feldspar, pyroxene, and often olivine

Basalt

Mafic volcanic rock (primarily Plagioclase and Pyroxene)

Basalt

Basalt (Mafic volcanic rock)

Basalt

Basalt (Mafic volcanic rock)

Dark mafic rock, likely basalt

Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine

Black basalt pebble

Basalt; fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene with possible olivine

Vesicular Basalt

Vesicular Basalt (Aphanitic Mafic Igneous Rock)

Basalt

Basalt (Mafic Extrusive Igneous Rock)

Dark volcanic rock fragment (possibly basalt)

Basalt, a fine-grained mafic volcanic rock; identification is uncertain from the image

Basalt

Extrusive mafic igneous rock

Basalt

Basalt (containing mainly Plagioclase feldspar and Pyroxene)

Basalt

Mafic Igneous Rock (composed primarily of Plagioclase and Pyroxene)

Basalt

Mafic Volcanic Rock

Basalt with Quartz Vein

Basalt (fine-grained mafic igneous rock) with crystalline Quartz (SiO2)

Basalt with Calcite Veining

Aphanitic Mafic Igneous Rock (Basalt) with CaCO3

Basalt with Calcite Veins

Basalt (Mafic Volcanic Rock)

Weathered vesicular basalt (likely amygdaloidal basalt)

Basalt, composed mainly of plagioclase feldspar, pyroxene, and altered olivine; cavities may contain secondary zeolite, calcite, or silica

Dark basaltic rock fragment

Basalt, likely vesicular or weathered basalt; chiefly plagioclase, pyroxene, and possible olivine

Basalt Gravel

Aphanitic Mafic Igneous Rock

Basalt Pebble

Basalt (Mafic Extrusive Igneous Rock)

Basalt

Basalt (Mafic volcanic rock)

Okenite

Okenite, Ca3Si6O15·6H2O

Basalt

Basalt (extrusive igneous rock)

Dark volcanic rock, likely basalt

Basalt; predominantly plagioclase feldspar and pyroxene, commonly with minor olivine and magnetite

Basalt

Basalt (dominated by plagioclase feldspar and pyroxene minerals)

Basalt

Basalt (Vitreous to Aphanitic Mafic Igneous Rock)

Basalt

Extrusive Mafic Igneous Rock (composed primarily of Plagioclase, Pyroxene, and Olivine)

Basalt

Basalt (Mafic Extrusive)

Rounded purple-gray pebble

Undetermined fine-grained volcanic rock; possibly andesite or basalt

Basalt

Basalt (Mafic volcanic rock)

Tumbled dark stone, possibly basalt or black tourmaline

Most likely fine-grained basalt (plagioclase–pyroxene), though black tourmaline (schorl, NaFe3Al6(BO3)3Si6O18(OH)4) is also possible

Vesicular Basalt with Quartz/Chalcedony

Vesicular Basalt (primarily Plagioclase, Pyroxene, and Olivine with SiO2 infill)

Basalt

Basalt (Aphanitic Mafic Volcanic Rock)

Basalt

Mafic Igneous Rock (composed primarily of pyroxene and calcium-rich plagioclase)

Basalt

Extrusive mafic igneous rock

Basalt

Basalt (Mafic Aphanitic Igneous Rock)

Basalt

Mafic Igneous Rock

Vesicular basalt (possibly slag-like volcanic rock)

Basalt, predominantly plagioclase–pyroxene–olivine; exact identification is uncertain from the photograph

Small dark rock fragment

Uncertain; possibly weathered basalt or slag

Rounded basaltic river pebble

Basalt, likely vesicular/amygdaloidal basalt