what kind of crystalline solid is a grain of sand

A grain of sand is typically a crystalline solid , most often composed of quartz (silicon dioxide, SiO₂), which forms a highly ordered atomic lattice.

Quartz Dominance

Quartz grains endure weathering better than other minerals, making up the bulk of sand in rivers, beaches, and deserts. Their tetrahedral crystal structure —silicon atoms bonded to four oxygens—gives them hardness (7 on Mohs scale) and clarity under a microscope.

Not Always Uniform

While quartz is covalent network solid , sands vary:

• Beach sand : Often 90%+ quartz, rounded by waves.
• Desert sand : Angular quartz from wind erosion.
• Volcanic areas : Basalt fragments or olivine (ionic crystals).
• Rare types include coral (calcite, ionic) or garnet (complex silicates).

Sand Type| Primary Mineral| Crystal Class| Key Trait
---|---|---|---
Inland/Beach| Quartz (SiO₂)| Covalent network| Weather-resistant 3
Volcanic| Olivine/ Pyroxene| Ionic/nesosilicate| Dark, glassy 3
Shell-based| Calcite (CaCO₃)| Ionic| White, fragile 3

Crystalline vs. Amorphous

Sand grains aren't amorphous like glass; they show distinct facets and cleavage planes from atomic order. Piles of sand flow granularly, but each grain is rigidly solid.

TL;DR : Primarily quartz—a durable covalent crystalline solid. Variations exist, but crystallinity defines the grains.

Information gathered from public forums or data available on the internet and portrayed here.