Cotterite: Historical review; extant specimens; etymology of ‘Cotterite’ and the genealogy of ‘Miss Cotter’; new observations on the Cotterite texture

Abstract

Abstract:‘Cotterite’ is a varietal name for an extremely rare form of quartz that displays a distinctive pearly metallic, but not vitreous, lustre. Originally discovered in a horizontal vein of calcite, quartz and ferruginous mud that crosscut Carboniferous limestone in a quarry at Rockforest (near Mallow, County Cork, Ireland) by ‘Miss Cotter’ in 1875/76, this quartz variety has been the subject of only two scientific papers, the second of which was by Professor Robert Harkness (then of Queen's College Cork) who named the variety in 1878. Genealogical research reveals that the mineral's dedicatee was Grace Elizabeth Cotter (1830–79), first-born daughter of Reverend George Edward Cotter (third son of the second Baronet Cotter of Rockforest) and Grace La Touche. Both father and daughter were involved in distributing specimens to Irish and British institutions. Currently, some 34 cotterites from Rockforest are extant. There are also two quartz's labelled as cotterite from Nova Scotia (Canada) and two from Devon (England). New observations reveal that cotterite's lustre results from light reflections off partial delamination structures and microfracture crazing patterns within the many late-stage lamellar-style quartz growth layers that comprise cotterite quartz's pyramidal faces.