Hematite

Hematite is a heavy, metallic iron oxide mineral that is the most important ore of iron. Its name comes from the Greek word 'haima', meaning blood, because even though it looks silver or black, it leaves a bright blood-red streak when rubbed on a hard surface. It is famous for its high density and its brilliant, mirror-like metallic luster when polished.

Formation & Geology

Hematite forms in a variety of environments: in enormous sedimentary beds (Band Iron Formations), as a primary mineral in igneous rocks, and as a product of hydrothermal activity. It is basically rust that has been compacted and crystallized over millions of years. It is found all over the solar system; the red color of the surface of Mars is caused by pervasive hematite dust.

Physical Characteristics

Hematite has a hardness of 5.5 to 6.5 and is very dense and heavy. It has a metallic to dull luster and is completely opaque. While it often forms in massive earthy lumps (red ocher), it can also grow in beautiful 'specular' sheets (like mirrors) or in rounded, kidney-shaped masses called 'kidney ore'. Its most distinctive diagnostic feature is its reddish-brown streak.

Historical & Industrial Significance

Hematite was the world's first pigment. Red ocher (earthy hematite) has been used in cave paintings for 40,000 years. Ancient Egyptians used specular hematite as actual mirrors. Today, it remains the primary source of iron for the world's steel industry. In jewelry, it is polished into beads and cabochons that look like silver-black metal. It is also used in the 'hematite' rings sold in gift shops (most of which are actually a synthetic material called hemalyke).