Minerals and geology of central Canada : comprising the provinces of Ontario and Quebec"
- Streak. Under this technical term is comprised the appearance or colour of the scratch, produced by drawing or " streaking " a mineral across a file or piece of unglazed porcelain. The character is a valuable one on account of its uniformity : as no matter how varied the colour of a mineral may be in different specimens, the streak will remain of one and the same colour throughout. Thus, blue, green, yellow, red, violet, and other specimens of fluor spar, quartz, &c., exhibit equally a white or "uncoloured" streak. The streak is sometimes " unchanged," The streak is sometimes " unchanged," or of the same tint as the external colour of the mineral ; but far more frequently it presents a different colour. Thus, whilst Cinnabar, the ore of mercury, has a red colour and reS streak, Realgar, red sulphide of arsenic, has a red colour and orange-yellow streak ; Copper Pyrites, a brass-yellow colour, and greenish-black streak ; and so forth. In cer- tain malleable and sectile minerals, the scratched surface presents an increase of lustre. The streak is then said to be " shining." Finally, it should be remarked, that in trying the streak of very hard minerals, we must crush a small fragment to powder, in place of using the file; because otherwise, a greyish-black streak, arising from the abrasion of the file, might very possibly be obtained, and so conduce to error.
https://archive.org/stream/mineralsgeologyo00chapuoft/minera...


INSTITUT ZA RUDARSTVO I METALURGIJU BOR
- Ugalj je sličnih mineraloško-petroloških karakteristika, mrko-crne boje, bez sjaja-mat, čokoladnog ogreba. Ravnog i glatkog preloma. Trakaste teksture, slabe ugljenifikacije, različite strukture.
- Coal has similar mineralogical-petrological characteristics, brownish-black, dull-matte, chocolate scratch, flat and smooth fracture, banded texture, weak carbonification of various structure.
https://scindeks-clanci.ceon.rs/data/pdf/1451-0162/2013/1451...