Synthetic Material (Not A Rock Or Mineral)

Limestone

Calcium Carbonate (CaCO3)

Quartzite

Metamorphic Quartzite (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.

Quartz (in a rock matrix)

Quartz (SiO2)

Fossiliferous Limestone

Carbonate Sedimentary Rock (primarily CaCO3)

Ferruginous Sandstone (Ironstone)

Ferruginous arenite

Granite Water-Worn Pebble

Intermediate to Felsic Plutonic Rock (Granite)

Polymict conglomerate with a projecting pebble

Conglomerate; clast-supported polymict conglomerate, dominated by quartz/feldspar and lithic fragments in a cemented matrix

Scoria (Vesicular Basalt)

Extrusive mafic igneous rock (high vesicularity)

Sandstone

Arenite (composed primarily of SiO2)

River Cobble (Quartzite with Iron Staining)

Metamorphic Quartzite (SiO2 with Fe2O3 inclusions)

Chert (specifically Jasper/Flint)

Microcrystalline Quartz (SiO2)

Banded Calcite (often sold as Mexican Onyx or Aragonite)

Calcite/Aragonite (Calcium Carbonate, CaCO3)

Quartzite Pebble

Quartzite

Chert (Arrowhead or Projectile Point)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Carnelian Beads

Silicon Dioxide (Variety of Chalcedony), $SiO_2$

Diorite

Diorite (Intermediate intrusive igneous rock)

Vesicular basalt (possible scoria)

Basaltic volcanic rock; chiefly plagioclase, pyroxene, and iron-rich minerals, with vesicles formed by trapped gas

Granite

Granite (plutonic igneous rock)

Red Granite

Phaneritic Felsic Igneous Rock

Conglomerate

Conglomerate (clastic sedimentary rock)

Petrified Wood

Silicified wood (primarily SiO2)

Milky Quartz Chip

Silicon Dioxide (SiO2)

Chert (Field Stone)

Microcrystalline / Cryptocrystalline Quartz (SiO2)

Rose Quartz

Quartz (SiO₂), specifically a variety of Quartz

Agate

Silicon Dioxide (Chalcedony), SiO2

Chert (variously Flints)

Microcrystalline Quartz (SiO2)

Chert (Red Jasper variant)

Microcrystalline Quartz (SiO2)

Feldspar Granodiorite

Granodiorite (Na,Ca)(Si,Al)4O8

Chert (and Jasper) Nodules in Limestone

Silicon Dioxide (SiO2) microcrystalline quartz

Chert (Flint Nodules)

Silicon Dioxide (SiO2)

Ferruginous Slag (Iron Smelting Byproduct)

Fused Silicate Scoria (Amorphous mixture of FeO, SiO2, and CaO)

River Stone (River Pebbles)

Alluvial Deposit (typically Quartzite, Sandstone, or Granite clasts)

Porphyritic Basalt or Porphyry

Porphyritic Igneous Rock

Laterite (iron-rich nodule, possibly Bauxite as a subtype)

Laterite (composed of various minerals including goethite, hematite, gibbsite, etc.)

Schist

Mica Schist

Basalt

Mafic Volcanic Rock (composed of Plagioclase Feldspar and Pyroxene)

Chert (Flint/Nodule)

Silicon Dioxide (SiO2)

Scoria (vesicular basalt)

Scoria; vesicular mafic volcanic rock, commonly basaltic in composition

Vesicular basalt (likely weathered scoria)

Basaltic volcanic rock; chiefly plagioclase, clinopyroxene, and olivine with vesicles

Conglomerate

Sedimentary Conglomerate

Rounded gray pebble

Indeterminate; likely a water-worn silicate or carbonate pebble