Field Work on Black Mountain

Black Mountain Open Space Park is a popular hiking and mountain biking destination.

Slightly metamorphosed andesites and basaltic andesites are present as gray to dark gray aphanitic (fine grained) rocks with scattered phenocrysts (crystals) of white plagioclase.

There are also volcaniclastic rocks like this tuff breccia that include large clasts of andesites, basaltic andesites, and fragmental volcanic rocks.

Outcrops of lapillistone contain accretionary lapilli, or rounded spheres of volcanic ash, that show evidence of the more turbulent and explosive nature of this volcano.

Hikers and bikers who visit Black Mountain may be less familiar with its volcanic history and more familiar with its mining history. In the 1920s, this area was briefly mined for arsenic. The arsenic was used in pesticides at the time (Stewart, 1963).

Our research group is exploring one of the abandoned mines.

In the mine waste, you can see shiny gold specs of aresenopyrite (FeAsS). Arsenopyrite is a sulfide mineral in which some of the sulfur is replaced with arsenic.

Amineh is studying trace element concentrations in the soils on Black Mountain. Here she is collecting samples. In the next few days, and over the course of the summer, we’ll show you how she processes these samples in the lab.

This was a small (~30 cm) rattlesnake that we saw earlier in the day, and we take field safety seriously, so when we heard a rattle coming from the tall grass, we ended our sampling and called it a day.