By: Ian Nicklin
Hematite is a common ore of iron that was extensively mined in northern England in the 19th century. The miners referrred to globular aggregates of hematite, such as this, as "kidney-ore" since it reminded them of the organ. We call this shape "reniform," which means the same thing: kidney-shaped.
The name "hematite," like the word "reniform," comes from the Greek heme, which means "blood." Although hematite typically appears black, thin pieces strongly backlit, will appear blood-red. Also, if you scratch a piece of hematite across some unglazed ceramic tile, it will leave a rouge-red streak. This is a diagnostic test for hematite.