What Makes a Rock an Ore
An ore is a rock that contains enough of a metal to be worth extracting. That is an economic definition, not a geological one, and it means the same mineral can be ore in one place and waste in another.
In the field, what you are actually identifying is the ore mineral — the specific sulphide, oxide or native metal that carries the metal. Most ore minerals are metallic or submetallic, which is a strong head start, because metallic lustre cuts the candidate list to about a dozen species.
The other useful fact is that ore minerals tend to be dense. They are heavy metal compounds, so a specimen that feels unexpectedly heavy for its size is a good candidate for ore.
The Ore Minerals You Are Most Likely to Find
These cover almost everything a hobbyist will meet in the field, and each is separated by streak plus one other test.
- Pyrite — iron sulphide, brassy gold, striated cubes, greenish-black streak. The most common ore mineral in the world.
- Chalcopyrite — copper iron sulphide, brassy with a greenish or purple tarnish, greenish-black streak. The main copper ore.
- Galena — lead sulphide, lead grey, very heavy, three directions of perfect cubic cleavage, lead-grey streak.
- Sphalerite — zinc sulphide, brown to black, resinous to submetallic, and it has six directions of perfect cleavage.
- Magnetite — iron oxide, black, strongly magnetic, black streak.
- Hematite — iron oxide, silver to red to black, always red-brown streak.
- Malachite and azurite — copper carbonates, vivid green and blue, soft, and they fizz in acid.
- Native gold — soft, heavy, and it marks paper without crumbling.
Streak Is the Decisive Test
For ore minerals, streak does more work than anything else. Rub the specimen on the unglazed back of a tile and read the powder colour.
Pyrite and chalcopyrite both streak greenish black, which separates them from gold, which streaks gold and is far softer. Hematite always streaks red-brown even when the specimen looks silver. Magnetite streaks black and is magnetic. Galena streaks lead grey. Sphalerite streaks pale yellow-brown to white.
That single test separates the two most commonly confused minerals in the field, pyrite and gold, and it costs nothing.
| Ore mineral | Metal | Hardness | Streak | The tell |
|---|---|---|---|---|
| Pyrite | Iron | 6–6.5 | Greenish black | Brassy, striated cubes. Harder than gold and it will not mark paper. |
| Chalcopyrite | Copper | 3.5–4 | Greenish black | Brassy with an iridescent tarnish. Much softer than pyrite, so a knife marks it. |
| Galena | Lead | 2.5 | Lead grey | Very heavy, soft, and it breaks into cubes along three perfect cleavages. |
| Sphalerite | Zinc | 3.5–4 | Pale yellow-brown | Resinous to submetallic, brown to black, with six directions of perfect cleavage. |
| Magnetite | Iron | 5.5–6.5 | Black | A magnet sticks firmly to it. Octahedral crystals. |
| Hematite | Iron | 5–6.5 | Red-brown | Red-brown streak whatever the specimen looks like, and often a submetallic sheen. |
| Malachite | Copper | 3.5–4 | Pale green | Banded vivid green with a silky sheen, and it fizzes in acid. |
| Native gold | Gold | 2.5–3 | Gold | Soft enough to mark with a knife, and heavy at specific gravity 15 to 19. |
Telling Gold From Pyrite
This is the single most common question in the field, and there are four quick answers.
Hardness: gold is 2.5 to 3, so a knife cuts it, while pyrite is 6 to 6.5 and will blunt the knife. Streak: gold streaks gold, pyrite streaks greenish black. Weight: gold is extraordinarily heavy at specific gravity 15 to 19 against pyrite at 5, so a gold nugget feels far heavier than a pyrite cube of the same size. Malleability: gold flattens under pressure, pyrite crumbles and powders.
One caution. Chalcopyrite is sometimes called fool’s gold too, and it is softer than pyrite, so a knife will mark it. Its greenish-black streak and its iridescent tarnish separate it from gold.
Field Kit for Ore Hunting
You need very little, and none of it is expensive.
- A magnet, for magnetite and for checking whether a black specimen is magnetic.
- An unglazed ceramic tile, for streak. The back of a bathroom tile works perfectly.
- A pocket knife, for hardness and for the gold test.
- A hand lens or a loupe, for cleavage, crystal form and striations.
- A small bottle of dilute acid, for the carbonate copper minerals.
A Note on Claiming and Collecting
Finding an ore mineral is not the same as finding a deposit. A visible sulphide in a rock does not mean there is enough metal to be worth anything, and most mineral occurrences are far too small to matter commercially.
It also matters where you are. Collecting is restricted or prohibited in national parks, on most mining leases and on private land without permission, and rules differ between states. Check before you take anything, and never dig on a lease.
The Bottom Line
Ore minerals are metallic or submetallic, usually dense, and identified by streak plus one other test. Pyrite and chalcopyrite streak greenish black, hematite red-brown, magnetite black, galena lead grey, sphalerite pale yellow-brown.
Gold is soft, heavy and malleable, and it streaks gold. If a knife does not cut it and it powders rather than flattens, it is not gold.
For related guides, see gold in rocks identifier and gold ore identifier. Pyrite identifier covers fool’s gold in detail, and hematite glittery black sparkly rock identifier covers the black metallic oxides.
Frequently Asked Questions
Start with streak, because it is decisive for ore minerals. Then add one more test — magnetism for magnetite, acid for the copper carbonates, cleavage for galena and sphalerite, or hardness for the gold test.