jacutingan.

1846 Trans. Royal Geol. Soc. Cornwall VI. 227 In both mines [sc. Itabira and Santa Anna, in Brazil] the directions and inclinations of the gold-bearing beds conform to the configuration of the neighbouring mountain, as well as to the structure of the contiguous rock;—a circumstance of common occurrence in jacotinga formations.

1851 Edinb. New Philos. Jrnl. 50 61 These [strata] are followed by the Jacotinga, the principal auriferous rock, which is for the most part composed of specular iron-ore and oxide [printed oixide] of manganese.

1869 R. F. Burton Explor. Highlands Brazil I. 301 The mysterious Jacutinga. The name is evidently derived from the well-known Penelope called Jácu-tinga (P. Leucoptera) from the white spots upon its crested head and blue-black wings. This substance of iron-black, with metallic lustre, sparkles in the sun with silvery mica... The constituents are micaceous iron schist and friable quartz mixed with specular iron, oxide of manganese, and fragments of talc.

1876 Encycl. Brit. IV. 224/2 Most gold is afforded by..the rock called Itacolumite,..and by certain iron ores known as Itabirite and Jacutinga.

1908 J. M. Maclaren Gold 649 With the itabirite are associated thin beds..of sandy micaceous and limonitic iron-ore containing yellowish talc and earthy oxides of manganese. These beds are generally friable, and appear to be a decomposition product of itabirite. The rock is locally known as jacutinga.

1934 H. F. Bain & T. T. Read Ores & Industries S. Amer. vi. 112 In places this [sc. itabirite] contains narrow veins of native gold, or of gold-bearing quartz, giving rise to what are known as jacutinga ores, which are peculiar to Minas Geraes.

1963 Prof. Papers U.S. Geol. Surv. No. 341 -C. 104/2 The term ‘jacutinga’ is now used indiscriminately for soft high-grade hematite, soft itabirite, or both, depending entirely upon the locality within the Quadrilátero Ferrífero. In short, it has only a local, not a general meaning and should not be used in scientific description without precise definition.