Mineral, Sediment

Quartz Geode (with possible Manganese or Goethite coating)

Silicon Dioxide (SiO2)

Sandstone (likely Quartzose Sandstone pebble)

Arenite (primarily SiO2)

Pyrite

Iron Sulfide (FeS2)

Green Fluorite

Fluorite (Calcium Fluoride, CaF2)

Sandstone

Arenite (SiO2 principal)

Clear Quartz

Silicon Dioxide (SiO2)

Sandstone

Arenite (SiO2 based)

Gneiss (specifically a granitic gneiss cobble)

Gneiss (high-grade regional metamorphic rock)

Dyed Quartz (often sold as 'Blue Quartz' or 'Blue Agate')

Silicon Dioxide (SiO2) with artificial pigment

Greenstone (Amygdaloidal Basalt)

Amygdaloidal Basalt (frequently composed of Plagioclase Feldspar, Pyroxene, and Olivine with Chlorite inclusions)

Amygdaloidal Basalt

Vesicular-Amygdaloidal Basalt (Mafic Extrusive)

Bauxite

Bauxite (mixture of hydrous aluminum oxides: Al(OH)3 & AlO(OH))

Milky Quartz with Iron Staining

Quartz (Silicon Dioxide, SiO2)

Milky Quartz

Silicon Dioxide (SiO2)

Fluorite

Calcium Fluoride (CaF2)

Malachite

Copper carbonate hydroxide, Cu2CO3(OH)2

Granodiorite (or Granite) Pebble

Phaneritic Felsic Igneous Pebble

Malachite

Malachite (Copper Carbonate Hydroxide, Cu2CO3(OH)2)

Gneiss

High-grade regional metamorphic rock (Foliated)

Turquoise

Turquoise (CuAl6(PO4)4(OH)8·4H2O)

Quartz in Matrix (possibly Basalt or Siltstone host)

Silicon Dioxide (SiO2) in Host Rock

Sandstone Concretion with Quartz Center

Sedimentary Clastic Rock (SiO2 matrix with Quartz core)

Chrysocolla on Matrix

Hydrated copper phyllosilicate (Cu,Al)2H2Si2O5(OH)4·nH2O

Calcite (Yellow/Orange variety - sometimes called Honey Calcite)

Calcite

Red Sandstone

Arenite (Ferruginous Sandstone)

Milky Quartz with Mineral Inclusions

Quartz (Silicon Dioxide, SiO2)

Silver (Native Silver Mineral)

Ag (Native Silver), Alloyed 90% Ag / 10% Cu

General Rock and Mineral Collection (Center: Angelite / Blue Anhydrite)

Anhydrite (Calcium Sulfate, CaSO4)

Milky Quartz with Mineral Inclusions

Silicon Dioxide (SiO2)

Pearl (as a biogenic mineral/gemstone)

Calcium Carbonate (mostly Aragonite), CaCO3

Chrysocolla in Matrix

Chrysocolla (Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O)

Turquoise in Matrix

CuAl6(PO4)4(OH)8·4H2O (Hydrous phosphate of copper and aluminium)

Schist (Micaceous)

Mica Schist

Citrine

SiO2 (Silicon Dioxide)

Fluorite (Rainbow or Multi-colored Fluorite)

Fluorite (Calcium Fluoride - CaF2)

Hematite

Hematite (Fe2O3)

Turquoise and Hematite

CuAl6(PO4)4(OH)8·4H2O (Turquoise) and Fe2O3 (Hematite)

Quartz-veined Sedimentary Rock

Hydrothermally veined Clastic Sedimentary Rock (SiO2 veins in Matrix)

Sandstone (likely with Quartz Veining)

Arenite (primarily 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.

Fluorite (Rainbow/Purple Fluorite)

Calcium Fluoride (CaF2)

Slate

Foliated Metamorphic Rock (primarily composed of quartz, illite, chlorite, and micas)