Why does nobody talk about how long identifying hornblende actually takes?

I spent a solid 8 hours last Saturday trying to ID a dark mineral in a granite sample I found near Prescott. Everyone online just says "it's hornblende if it's black and elongated" like it's that simple. Problem is, biotite and augite look almost identical under a hand lens when the grain size is small. I had to do a streak test and check the cleavage angles under magnification to finally call it. How long did it take you to get confident with mafic mineral IDs?

2 comments

2 Comments

jenkins.wade1mo ago

My buddy Steve spent about 6 hours on a single sample from the Sierra Nevada once. He kept flipping it in the light thinking he saw bronzy flashes like biotite but the cleavage was all wrong. He finally gave up and drove it over to my place with a hand lens and a streak plate. We sat on the porch crushing a tiny piece and the streak came out pale gray, not black, so we knew it was hornblende. He still texts me pics of dark minerals to this day asking "biotite or hornblende" like a crazy person.

black.wesley29d ago

Ngl that buddy Steve is living in all our heads rent free. Honestly buying a streak plate was the best 8 bucks I ever wasted on a rock.