rosaker
/rəʊˈzakə/ /ˈrəʊzakə/(also rosacre) Now historical
noun
The mineral realgar (red arsenic).
Origin
Late Middle English; earliest use found in Geoffrey Chaucer (c1340–1400), poet and administrator. Apparently a variant of resalgar, perhaps influenced by rose on account of the red colour of the mineral's crystals.