Industrial Byproduct (Often Mistaken For Obsidian Or Mineral)

Iron Meteorite

Siderite (Iron-Nickel Alloy), predominantly Kamacite and Taenite (Fe, Ni)

Ferruginous Quartz (Iron-stained Quartz)

Silicon Dioxide (SiO2) with Hematite/Limonite impurities

Marble

Recrystallized Calcite (CaCO3) or Dolomite (CaMg(CO3)2)

Quartz Pebble

Silicon Dioxide (SiO2)

Milky Quartz with Iron Staining

Quartz (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.

Rough Quartz (Alluvial Pebbles)

Silicon Dioxide (SiO2)

Quartz (Milky Quartz)

Silicon Dioxide (SiO2)

Yellow Agate

Silicon Dioxide (SiO2)

Limonite (Iron-rich Siltstone / Sandstone base)

Hydrous ferric oxide mixture (FeO(OH)·nH2O)

Sandstone (Quartzose)

Arenite (SiO2 principal)

Pyrite (Fool's Gold)

Iron Sulfide (FeS2)

Lepidolite

Lepidolite (K(Li,Al)3(Al,Si,Rb)4O10(F,OH)2)

Lepidolite on Pegmatite

Lepidolite (K(Li,Al)3(Al,Si,Rb)4O10(F,OH)2)

Howlite

Calcium borosilicate hydroxide (Ca2B5SiO9(OH)5)

Polished Basalt

Basalt (Mafic volcanic rock)

Orthoclase Feldspar

KAlSi3O8 (Potassium Aluminum Silicate)

Quartz Pebble

Silicon Dioxide (SiO2)

Sapphire (Corundum)

Corundum (Al2O3), variety Sapphire

Sandstone (Red)

Arenite (composed primarily of SiO2)

Malachite

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

Ferruginous Sandstone (Gozzan)

Iron-rich clastic sedimentary rock with Limonite/Goethite

Glaucophane-bearing Schist (Blueschist)

Blueschist (Glaucophane-Lawsonite Schist)

Bay Scallop Shell

Argopecten irradians (Biogenic Calcium Carbonate / CaCO3)

Black Pearl (Tahitian Pearl)

Aragonite / Calcite (CaCO3) with Conchiolin

Iron-stained Quartz

Silicon Dioxide with Iron Oxide (SiO2 + Fe2O3/FeO(OH))

Howlite

Calcium borosilicate hydroxide (Ca2B5SiO9(OH)5)

Gold

Gold (Au)

Rhodochrosite

Manganese carbonate (MnCO3)

Prehnite

Prehnite, Ca2Al2Si3O10(OH)2

Hand-Drawn Trading Card (Amateur Artwork)

Cellulose-based substrate with wax/graphite/ink deposit (n/a for minerals)

Quartz (Iron-stained)

Silicon Dioxide (SiO2)

Quartz with Iron Oxide Inclusions

Silicon Dioxide (SiO2) with Hematite/Limonite

Diorite

Diorite (an intrusive igneous rock)

Green Fluorite

Calcium Fluoride (CaF2)

Green Fluorite

Fluorite (Calcium Fluoride) - CaF2

Fluorite

Calcium Fluoride (CaF2)

Amber

Succinite (fossilized resin)

Chert (specifically Flint or Jasper variant)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Honey Calcite

Calcium Carbonate (CaCO3)

Fluorite (Yellow and Multi-color)

Calcium Fluoride (CaF2)

Quartz Vein in Host Rock

Silicon Dioxide (SiO2) within Metasedimentary or Igneous matrix