The Collaborative International Dictionary of English v.0.48:

Hemin \He"min\, n. [Gr. a"i^ma blood.] (Physiol. Chem.)
   A substance, in the form of reddish brown, microscopic,
   prismatic crystals, formed from dried blood by the action of
   strong acetic acid and common salt; -- called also
   Teichmann's crystals. Chemically, it is a hydrochloride of
   hematin.
   [1913 Webster]

   Note: The obtaining of these small crystals, from old blood
         clots or suspected blood stains, constitutes one of the
         best evidences of the presence of blood.
         [1913 Webster]

WordNet (r) 3.0 (2006):

hemin
    n 1: a reddish-brown chloride of heme; produced from hemoglobin
         in laboratory tests for the presence of blood [syn:
         hemin, protohemin]