amphibole group of minerals.
"The Student's Elements of Geology"
Sir Charles Lyell
They are characterized by minerals of gold, tin, iron, titanium, zinc, and copper, and sometimes of tungsten and molybdenum, in a gangue of quartz, which contains also minerals such as garnet, corundum, amphibole, pyroxene, tourmaline, spinel, and mica.
"The Economic Aspect of Geology"
C. K. Leith
Both are common alteration products of magnesian silicate minerals such as olivine, pyroxene, and amphibole.
"The Economic Aspect of Geology"
C. K. Leith