Bloodstone

Bloodstone is a dark green chalcedony, a variety of jasper, spotted with red iron oxide. The green is from chlorite and amphibole inclusions, the red spots from hematite. Physically it is unremarkable: an opaque, tough, common material, easily carved, historically cheap.

Its other name is heliotrope, sun-turner, and the classical explanation is worth recording because it is so odd. Pliny reports that the stone, placed in a vessel of water, turns the reflection of the sun blood-red; and that magicians claimed that combined with a particular herb it conferred invisibility, a claim he treats with contempt as the sort of thing the magi say. The reflection effect is describable as an actual optical observation of a dark green stone in water; the invisibility is not.

The famous association is Christian and it can be dated to within the medieval period rather than to antiquity. The legend holds that bloodstone was formed at the Crucifixion, when blood from the wounds of Christ fell on green jasper at the foot of the cross. On the strength of it the stone became a martyr's stone, carved with scenes of the Passion and with the flagellation in particular, and a large number of such carvings survive from the fifteenth and sixteenth centuries.

The legend does not appear in the classical sources, which know the stone under a different name and a different story. It is a Christian reinterpretation grafted onto an existing material, and the graft is visible: the pagan optical wonder and the Christian relic-substitute coexist in the medieval literature without being reconciled.

The uses attributed to bloodstone are almost entirely governed by the red spots, and they make a clean case study in the doctrine of signatures applied to minerals rather than plants.

The stone was held to staunch bleeding: carried by soldiers, held in the hand or applied to a wound, and worn against nosebleed and haemorrhage. It was associated with the blood generally, with courage and endurance in battle, and with athletic strength. Every one of these follows from a visual resemblance and none of them follows from any property of iron-spotted chalcedony, which is inert.

This is the same reasoning that placed nettle under Mars for its sting or read the perforations of St John's Wort as sunlight. In the mineral kingdom the doctrine of signatures is if anything more transparently circular than in the plant kingdom, because a stone has no pharmacology at all to accidentally vindicate it. Willow bark contained an analgesic by chance; bloodstone contains nothing.

Bloodstone was the original March birthstone on the 1912 National Association of Jewelers list, paired with aquamarine, and the two were swapped in emphasis in the 1952 revision so that aquamarine became the primary March stone and bloodstone the alternative. That reshuffle is documented and commercial, and it is a useful demonstration that these lists are administrative rather than traditional: a stone does not stop having a March character because a trade council voted.

Bloodstone does appear in older month and sign correlations, where it is more usually attached to March and to Aries, and those correlations descend from the breastplate literature rather than from the modern chart.