Why basalt is the top candidate
Based on the photo: dark gray/black color, matte surface, very fine grain, and a smooth rounded shape consistent with water tumbling (river/beach). Light patches can be weathering or small mineral veins/infill.
Common look-alikes
- Chert / flint: often waxier/glossier, breaks with sharp conchoidal (shell-like) fractures.
- Slate: tends to split along flat layers (cleavage) more than it rounds smoothly.
- Hematite-rich stone: can look dark but often leaves a reddish-brown streak on ceramic.
What would make basalt less likely?
- If it scratches glass easily and feels “glassy” with sharp fractures → more like chert/flint.
- If it splits into thin plates or shows obvious layering → more like slate.
- If it leaves a strong rusty/red streak on unglazed tile → consider hematite.
At-home tests (safe + simple)
Rub the rock on the back of an unglazed ceramic tile (or the unglazed ring under a mug).
• Basalt: usually no strong colored streak (maybe light gray)
• Hematite: often reddish-brown
Try to scratch a glass bottle (gently). If it scratches glass easily, it may be harder materials like chert. Basalt can sometimes scratch glass, but chert is more consistently “glass-scratching” and often looks waxier.
Use a phone macro lens or magnifier. Basalt often shows tiny mineral grains; chert looks very uniform and “smooth.”
If you want a near-certain ID: a local rock shop/geology department can do a quick check, or you can send me:
where found, streak result, and magnet result.