Mineral (Man Modified)

Dendritic Opal (Common Opal)

Amorphous Hydrated Silica (SiO2·nH2O) with Manganese or Iron Oxide inclusions

Diamond

Diamond (Carbon, C)

Peridot (likely, given the color and bead form)

Olivine, variety Peridot (Mg,Fe)2SiO4

Build-A-Bear Plush (Non-Geological)

Polyester fibers (C10H8O4)n and Synthetic Polymers

Sandstone Geode (Ironstone Concretion)

Arenite with Limonite/Hematite matrix (SiO2 with Fe-oxides)

Granite

Phaneritic Felsic Igneous Rock

Fluorite-Gedrite in Quartz (Schist)

Fluorite (CaF2) with Gedrite in Quartz/Feldspar Matrix

Yellow Quartzite River Cobble

Meta-quartzite (SiO2 with iron oxide staining)

Amber

Succinite (fossilized tree resin)

Amber

Succinate (Fossilized Tree Resin)

Basaltic Tuff / Volcanic Breccia

Pyroclastic Breccia / Lithic Tuff

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

Serpentine (Serpentinite)

Serpentinite (complex silicate group including lizardite, chrysotile, and antigorite)

Sandstone (Ferruginous)

Clastic sedimentary rock (primarily SiO2 with Fe2O3 cement)

Sandstone (Ferruginous)

Arenite (Fe-rich)

Granite Cobble

Felsic Intrusive Igneous Rock (composed of Quartz, Alkali Feldspar, and Plagioclase)

Granite

Phaneritic Igneous Rock (primarily Quartz, Feldspar, and Mica)

Serpentinite

Serpentinite (composed primarily of Serpentine minerals: Mg3Si2O5(OH)4)

Amber

Succinite (Fossilized Tree Resin)

Banded Sandstone

Arenite (composed primarily of Quartz: SiO2)

Pearl (Imitation or Cultured)

Calcium Carbonate (Aragonite/Calcite) - CaCO3

Chert (Chert / Flint nodule)

Silicon Dioxide (SiO2)

Chert (Grey Chert)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Quartzite (Milky Quartz Cobble)

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.

Chert (specifically Banded Chert)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Petrified Wood

Silicified Wood (SiO2)

Sandstone (Quartz-rich Pebble)

Arenite (primarily SiO2)

Sandstone (with Iron Staining)

Arenite (composed primarily of SiO2 with Fe2O3 staining)

Sandstone

Arenite (composed primarily of SiO2)

Sandstone (Ferruginous)

Arenite (primarily SiO2 with Iron Oxide cement)

Sandstone (with Liesegang rings or Oxidation)

Arenite (primarily Quartz SiO2 with Iron Oxide Fe2O3 staining)

Sandstone (Quartzose)

Arenite (primarily SiO2)

Serpentinite

Serpentinite (composed primarily of Serpentine group minerals: (Mg,Fe)3Si2O5(OH)4)

Granite Pebble (Salt and Pepper Granite)

Felsic Intrusive Igneous Rock (Granite)

Petrified Wood

Silicified Wood (SiO2)

Sandstone

Sandstone (lithified quartz arenite, arkose, graywacke, etc. depending on composition)

Amethyst Sage Agate

Silicon Dioxide (SiO2) with trace minerals (Manganese/Iron oxides)

Rose Quartz

Quartz (SiO₂), specifically a variety of Quartz

Milky Quartz with Mineral Inclusions

Quartz (Silicon Dioxide, SiO2)

Granite

Granite

Chert (Nodular Chert)

Microcrystalline Silica (SiO2)