Not A Rock Or Mineral

Green Aventurine

Aventurine (variety of Quartz - SiO2)

Ferruginous Sandstone (Gozzan)

Iron-rich clastic sedimentary rock with Limonite/Goethite

Serpentinite

Serpentinite (composed primarily of Serpentine group minerals, Mg3Si2O5(OH)4)

Opal

Hydrated Amorphous Silica (SiO2·nH2O)

Travertine (Calcareous Tufa)

Calcium Carbonate (CaCO3)

Amygdaloidal Rhyolite (often called Lake Superior Agate relative)

Rhyolite with Calcite/Quartz amygdules (SiO2 and secondary minerals)

Vesicular Basalt (Scoria)

Extrusive Mafic Volcanic Rock (FeO-SiO2-MgO)

Laterite

Laterite (no specific mineral formula as it's a rock type)

Basalt

Afanitic Mafic Basalt

Basalt

Mafic volcanic rock (primarily plagioclase, pyroxene, and olivine)

Prehnite

Prehnite - Ca2Al(AlSi3O10)(OH)2

Granitic Gneiss

Gneiss (High-grade regional metamorphic rock)

Conglomerate

Conglomerate (Detrital sedimentary rock)

Basalt

Extrusive mafic igneous rock; primarily (Ca,Na)(Mg,Fe,Al,Si)2O6 with (Ca,Na)(Al,Si)4O8

Chert (Commonly known as Flint)

Microcrystalline Quartz (SiO2)

Jasper with Quartz inclusion

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Beryl (likely Aquamarine) in matrix

Be3Al2(SiO3)6 (Beryllium Aluminum Silicate)

Amethyst Geode (Carved)

Amethyst (Violet Crystalline Quartz - SiO2)

Calcite on Limestone (or Fossil)

Calcium Carbonate (CaCO3)

Banded Gneiss

Gneiss (High-grade Metamorphic Rock)

Ironstone Concretion / Goethite Nodules

Ironstone (composed primarily of Goethite FeO(OH) and Limonite)

Ironstone Concretion (Limonite/Goethite)

Goethite-rich Concretion (FeO(OH))

Green Quartzite (Aventurine-like)

Quartzite (primarily SiO2 with chromium-rich mica or chlorite inclusions)

Porphyry (Flower Stone)

Porphyritic Basalt or Andesite

Chert (Nodule/Pebble)

Chert (Silicon Dioxide, SiO2)

Basalt with Plagioclase Phenocrysts

Porphyritic Basalt

Conglomerate

Conglomerate (Detrital Sedimentary Rock)

Vesicular Basalt (Scoria)

Vesicular Basalt

Fossilized Gastropod (Snail)

Class Gastropoda (internal mold or 'steinkern')

Ocean Jasper (Orbicular Jasper)

Silicon Dioxide (SiO2) with iron and other impurities

Given the appearance, it's likely a fragment of an igneous or metamorphic rock composed of multiple minerals. Without specific diagnostic features, it's difficult to give a common name other than 'crystalline rock fragment'. If pressed to guess based on the granular, somewhat light and dark speckled appearance, it could be a fragment of granite or a related intrusive igneous rock.

As a rock fragment, it does not have a single scientific mineral name; rather, it's a piece of a rock which is a combination of minerals. If it were granite, its main mineral composition would be quartz (SiO2), feldspar (e.g., KAlSi3O8 - orthoclase, (Na,Ca)(Al,Si)4O8 - plagioclase), and mica (e.g., KAl2(AlSi3O10)(OH)2 - muscovite or K(Mg,Fe)3AlSi3O10(OH)2 - biotite), among others.

Schist

Mica Schist

Green Aventurine (Green Quartzite)

Silicon Dioxide (SiO2) with inclusions of Fuchsite (K(Al,Cr)2(AlSi3O10)(OH)2)

Sandstone

Arenite (primarily SiO2 - Silicon Dioxide)

Sandstone

Arenite (composed primarily of SiO2)

Pink Granite with Quartz Vein

Phaneritic Plutonic Felsic Rock (K-feldspar + Quartz + Plagioclase + Mica)

Red Sandstone

Clastic sedimentary rock (primarily SiO2 with Fe2O3)

Pebble (likely Quartzite or Chert)

Clastic Sediment, potentially composed of SiO₂ (Quartz)

Druzy Quartz (on Geode Fragment)

Silicon Dioxide (SiO2)

Quartz

Quartz (SiO2)

Schist

Mica Schist

Ferruginous Sandstone (River Pebble)

Clastic Sedimentary Rock (primarily SiO2 with Fe2O3 cement)