A significant locality and species specimen of this very interesting, quite rare, crystallized sodium aluminum fluoride species. The crystals look like cityscape blocks with gem clear cubes slightly elevated from the massive matrix (matrix and aspect looking like cryolite is supposed to, rather than like pseudocubic thomsenolites which can appear similar). One cryolite crystal is 1.5cm across! Dark brown-black rhombohedrons of siderite to 1 cm are scattered within the cryolite matrix as shown on the shot of the rear contact face. The cryolite deposits at Ivigtut were mined for aluminum and were one of world's earliest sources of that element during the late 19th Century through the early 20th Century! This place was basically stripmined under water level, to get at the deposit, before bauxite smelting was used to recover aluminium, and such large specimens are few and far between today, in any quality. A historic, important, rarity.