Sedimentary Rock (Specifically A Concretion Or Possibly A Geode)

Mica Schist

Mica Schist (primarily Muscovite and Quartz)

Serpentine (Serpentinite)

Antigorite, Lizardite, or Chrysotile (Mg,Fe,Ni,Al,Zn,Mn)2-3(Si,Al,Fe)2O5(OH)4

Quartz (likely milky quartz or a stained variety)

Silicon Dioxide (SiO₂)

Chert (Jasper focus)

Silicon dioxide (SiO2) - Microcrystalline Quartz

Basalt (Concrete Aggregate)

Basalt (Mafic volcanic rock)

Milky Quartz

Silicon Dioxide (SiO2)

Amethyst

Silicon Dioxide (SiO2) with iron impurities

Quartz Geode with Goethite/Hematite

Silicon Dioxide (SiO2) with Iron Oxides

Dyed Quartz Geode

Silicon Dioxide (SiO2) with artificial pigment

Shale or Slaty Mudstone

Argillaceous sedimentary rock

Amethyst

Silicon Dioxide (SiO2) with iron impurities

Quartzite (Milky Quartz Cobble)

Silicon Dioxide (SiO2)

Chert (specifically Gray Chert)

Chert (SiO2)

Greywacke (River Slikkenstone)

Greywacke (Impure Sandstone)

Amethyst

Silicon Dioxide (SiO2) with iron impurities

Amethyst

Amethyst (SiO2 - Silicon Dioxide with iron impurities)

Red Jasper (possibly Chert/Argillite)

Jasper (SiO2) with iron oxide inclusions

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.

Amethyst (Quartz)

Silicon Dioxide with Iron impurities (SiO2)

Granite

Granite (Felsic Plutonic Rock)

Montana Moss Agate

Chalcedony (Silicon Dioxide, SiO2)

Amethyst

Amethyst (Silica mineral, SiO2)

Amethyst (Tumbled)

Amethyst (Silicon Dioxide, SiO2 + Fe4+)

Prehnite

Prehnite - Ca2Al(AlSi3O10)(OH)2

Amethyst

Amethyst (Silicon Dioxide, SiO2)

Banded Agate (specifically Carnelian Agate)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Granite Pegmatite

Phaneritic Plutonic Igneous Rock

Amethyst

SiO2 (Silicon Dioxide with Iron impurities)

Granite (Pink Orthoclase variety)

Phaneritic intrusive igneous rock (Quartz, Orthoclase, Plagioclase, and Mica)

Pink Granite (with Potassic Feldspar and Quartz)

Felsic Intrusive Igneous Rock (Granite)

Pink Granite

Granite (Phaneritic igneous rock rich in Alkali Feldspar and Quartz)

Red Jasper with Quartz

Silicon Dioxide (SiO2) with Hematite inclusions

Fancy Jasper

Silicon Dioxide (SiO₂)

Quartz

Silicon Dioxide (SiO2)

Schist (specifically Chlorite/Greenschist)

Chlorite Schist

Emerald in Matrix (Quartz/Schist)

Beryl (Be₃Al₂Si₆O₁₈) with Chromium/Vanadium impurities

Amethyst

Silicon Dioxide (SiO2) with iron impurities

Greywacke (River Siltstone)

Lithic Wacke (Sandstone subfamily)

Quartz Veined Basalt

Mafic Volcanic Rock with Microcrystalline Quartz (SiO2)

Chert (also known as Flint or Common Chalcedony)

Cryptocrystalline Silica (SiO2)

Quartz (Milky Quartz)

Silicon Dioxide (SiO2)

Scoria (Red Lava Rock)

Scoria