Hallefinta

Hallefinta (Swedish), a very hard compact rock, yellow, red, brown, green, gray, or black. It is composed of an intimate mixture of siliceous and felspathic matter, with occasionally scales of chlorite or mica. In hand-specimens it might be readily mistaken for a compact felsite, but in good sections in the field it generally occurs in thin beds and bands. It appears to be a metamorphic rock—in some cases an altered volcanic mud.