Igneous, Sedimentary, Or Metamorphic (Mineral Based)

Quartz / Quartzite Fragment

Silicon Dioxide (SiO2)

Gold Mineral

Native Gold (Au)

Agate

Silicon Dioxide (Chalcedony), SiO2

Biotite Mica

Biotite (K(Mg,Fe)3AlSi3O10(OH,F)2)

Quartz

Silicon Dioxide (SiO2)

Green Gneiss or Greenschist

Chlorite/Actinolite Gneiss or Schist

Black Spinel

Magnesium Aluminum Oxide (MgAl2O4)

Gravel / Small Pebble

Rock Fragment (Gravel)

Quartz (Milky Quartz)

Silicon Dioxide (SiO2)

Pyrite

Iron Pyrite (FeS2)

Geode (Unopened)

Quartz/Chalcedony concretion

Pyrite (on Quartz/Host Rock)

Iron Sulfide (FeS₂)

Orange Calcite

Calcium Carbonate (CaCO3)

Gold

Native gold (Au)

Coarse Sand or Fine Gravel

Detrital Sedimentary Fragments (mostly SiO2)

Yellow Apatite

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

River Pebble (Gneiss or Quartzite mixture)

Metamorphic rock (Commonly Gneissic)

Gneiss

Gneiss (High-grade metamorphic rock)

Blue Sapphire (in a faceted jewelry setting)

Corundum (Al2O3) with trace Iron and Titanium

Muscovite Mica

Muscovite KAl2(AlSi3O10)(OH)2

Red Garnet

Pyrope or Almandine (Silicate group, X3Y2(SiO4)3)

White Quartz (Milky Quartz)

Silicon Dioxide (SiO2)

Mica

Mica group (often Muscovite or Biotite)

Aquamarine

Beryl (Be3Al2Si6O18 with iron impurities)

Smoky Quartz Cluster

Smoky Quartz (Silicon Dioxide - SiO2)

Quartz

Silicon Dioxide (SiO₂)

Water and Silt (Sedimentary Environment)

Suspended Sediment / H2O (dihydrogen monoxide)

Bronzite

Enstatite (magnesium iron silicate), (Mg,Fe2+)SiO3

Black Tourmaline (Schorl)

Schorl (Sodium iron silicate hydroxide boron silicate); NaFe3Al6(BO3)3Si6O18(OH)4

Quartz / Quartz Cluster

Silicon Dioxide (SiO2)

Milky quartz

Quartz (silicon dioxide, SiO₂)

Mica (Muscovite or Biotite)

Sheet silicate mineral group (e.g., KAl2(AlSi3O10)(F,OH)2)

Schist

Schist (Crystalline Metamorphic Rock)

Chalcedony (Grey/White Agate)

Silicon Dioxide (SiO₂)

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.

Iolite (Cordierite)

Cordierite (Magnesium Aluminum Silicate), Mg2Al4Si5O18

Blue Kyanite

Kyanite (Al2SiO5)

Blue Sapphire

Corundum (Al2O3)

Blue Kyanite

Kyanite (Al2SiO5)

Ruby / Pink Sapphire

Corundum (Al2O3 with Chromium impurities)

Greenstone (Greenschist facies)

Greenschist (composed primarily of Chlorite, Actinolite, and Epidote)

River Pebble

Weathered Rock Fragment