Identifying jet and shale
Black, warm, and lightweight.
Jet is fossilised wood — black, lightweight, and warm to the touch, taking a high polish. Rubbed on unglazed ceramic it leaves a brown streak; rubbed briskly it can hold a static charge. Whitby in Yorkshire was the great source, worked from prehistory through the Victorian mourning-jewellery boom.
Shale is duller, heavier-feeling, and more prone to laminar cracking; it leaves a similar streak but takes a lesser polish. Both were carved into beads, rings, and pendants, notably in Roman and prehistoric Britain.
The common impostors tell on themselves: black glass is cold, heavy, and streakless; vulcanite and early plastics show mold seams and smell of rubber or camphor when warmed by friction.
Record “jet or shale” when the streak and feel leave doubt — the two were used side by side, and honest uncertainty is the accurate answer.