Mineral IdentificationThe Sulfides

These are not common minerals but are prized because of their economic value.

Geologists often make these minerals the target of their exploration.

These minerals are the source of many metals we use today.

These minerals must be refined to separate the metal from the sulfur

The properties they share are metallic lustre, high specific gravity (heavy) and streak.

The Sulfides

Remember to streak all metallic minerals Have a magnet handy as some sulfides are

magnetic. Remember to wash your hands after

handling due to the presence of heavy metals.

Identification notes

PROPERTY

Colour Caramel brown to Black

Crystal Form rare

Cleavage/Fracture Common in 6 directions – as a result the small grains have many smooth cleavage faces which cause the mineral to sparkle!

Lustre Sub-metallic – can be somewhat vitreous

Hardness Soft (4)

Specific Gravity heavy

Streak Brown to black (few minerals streak brown – the other you know is Chromite)

Other Commonly found with Galena (and even Chalcopyrite) in limestone.It is the main ore of zinc (used to galvanize steel)

19) Sphalerite (ZnS)

PROPERTY

Colour Brassy yellow

Crystal Form Common (cubes, pyritohedrons, striated crystals) but is usually seen massive

Cleavage/Fracture none

Lustre Metallic

Hardness Very hard (7) – can scratch glass – unusual for a metallic mineral

Specific Gravity Medium-heavy

Streak black

Other Non-magneticThe most common metallic mineral !– often called “fools gold” due to its brassy colour (this mineral shares almost no other properties with gold)Despite its abundance it has no economic value – most iron ores are iron oxides. It is indicator mineral in many gold mines.

20) Pyrite (FeS2)

PROPERTY

Colour Gun-metal grey

Crystal Form Common (cubes, pyritohedrons, striated crystals) but is usually seen massive

Cleavage/Fracture Perfect in 3 directions 90˚ creating cubic cleavage fragments

Lustre Metallic – very lustrous cleavage faces

Hardness Soft (3) – soft – easily scratched by a nail

Specific Gravity Very heavy due to the lead – densest mineral in our set.

Streak black

Other Commonly associated with sphalerite.Galena “rusts” to a duller greyNon-magneticIt is the main ore of lead in the world

21) Galena (PbS)

PROPERTY

Colour Yellow-gold – the colour is more yellow than pyrite but less golden than gold.

Crystal Form Almost always massive

Cleavage/Fracture none

Lustre Metallic

Hardness hard (4.5) – cannot scratch glass – can be scratched with a nail

Specific Gravity Medium-heavy

Streak black

Other Non-magneticThe problem is that it is often associated with pyrrhotite which is magneticIt is a major ore of copper. Used for wiring and pipes.

22) Chalcopyrite (CuS2)

PROPERTY

Colour Brownish metallic

Crystal Form Usually massive but can form hexagonal prismatic crystals.

Cleavage/Fracture none

Lustre Metallic

Hardness hard (5) – cannot scratch glass – can be scratched with a nail

Specific Gravity Medium-heavy

Streak black

Other MagneticIt is often associated with similarly coloured pyrite and chalcopyriteOdd formula is due to Fe atoms that are often absent in the crystal structure.It has little economic value

23) Pyrrhotite (Fe1-xS)

PROPERTY

Colour Black sub-metallic to purplish metallic with a common irridescent coloured surface leading to its nickname of “Peacock Ore”

Crystal Form Usually massive

Cleavage/Fracture none

Lustre Metallic-Sub-metallic

Hardness soft (4) – cannot scratch glass – can be scratched with a nail

Specific Gravity Medium-heavy

Streak black

Other Non-MagneticAlmost always has a greenish “rust”It is often associated with other copper sulfides such as chalcopyriteIt is a secondary ore of copper

24) Bornite (Fe5CuS4)