An iron ore that is found in many forms, e.g. (1) in massive form, and when showing a metallic luster called 'specularite'; (2) in botryoidal or nodular form, sometimes called 'kidney stone'; (3) in druses of crystals, especially in Cumberland (now Cumbria), England; and (4) as thin, transparent flakes which form a many-petalled rosette, called an 'Alpine rose' or 'iron rose'. It is blue-black, but when in fragments or powder it is blood-red (hence the name, from the Greek haema, blood), and when the stone is rubbed on an unpolished surface it leaves a red streak. It has been used in jewelry since Egyptian times, as a seal carved in intaglio, as a cameo on a signet ring (often depicting a warrior's head), as a cabochon set in a pendant or finger ring, and as beads strung in a bracelet or necklace (sometimes to imitate a black pearl). It is found as an inclusion in some aventurine quartz and sunstone. Sometimes called 'iron glance', owing to its metallic luster.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson