Copper
Cu · Cubic · also called native copper
Native copper is one of the very few metals that occurs naturally in usable metallic form, which is why it was the first metal humans worked. Michigan's Keweenaw Peninsula produced it in masses weighing tonnes.
Properties
- Mohs hardness
- 2.5–3
- Streak
- copper red
- Lustre
- metallic
- Colour
- Fresh surfaces are bright copper-red; exposed surfaces tarnish brown, then to green malachite crust.
- Cleavage
- No cleavage; it deforms instead.
- Fracture
- Hackly
- Specific gravity
- 8.9–8.95 (water = 1)
- Magnetism
- Not magnetic
- Acid test
- No reaction
- UV
- Not fluorescent
Tests that confirm copper
- Malleable — it bends and flattens rather than breaking.
- Copper-red streak.
- Heavy, and often found as twisted wire-like or branching masses.
What copper gets confused with
Each of these is settled by one test. Run that test first.
Bronze or brass scrap
Manufactured metal shows tool marks, casting seams, or uniform machined shapes.
Chalcopyrite is brittle and brass-yellow; copper is malleable and red.
Where it is found
Basalt flows and their cavities, and the oxidised zones of copper deposits.
Is it worth anything?
Attractive crystallised and branching specimens have solid collector value; massive lumps less so.