For some of us, this summer has been one of our first exposures to field geology, and sometimes it feels like a crash course in geology as we learn something new each day. Mike has been incredibly patient with us and we've been picking up some mineral identification skills.
Biotite is one of the more common minerals that we've seen in the rocks we've been working with. It's a mineral in the mica group, meaning that it is a sheet silicate and grows in platy crystals. It is usually a dark brown or blackish spot in the rocks that we see and easy to pick out if we can spot the flaky crystals.
Feldspars are another class of minerals that have been extremely common in our adventures. Plagioclase (a type of feldspar) is typically easy to identify because it is a clean, white, opaque mineral in the rock. Things start to get a little confusing though when we wonder whether there are two types of feldspars in the rock... Although K-spar is typically pink in color, it can also appear to be white or grey with a degree of translucency. So adding this to a rock that is already composed of minerals that are grey, white and black... Things can get a little confusing.
Quartz is in almost every rock we've seen so far, and it's usually a colorless, greyish crystal. Sometimes it's tough to tell it apart from a grey feldspar, but we've learned that feldspars will usually have reflective crystal faces that glint in the sun while quartz crystals are more glassy and won't have the reflective faces.
Some of the rocks we've looked at had hornblende crystals (dark, needle-like crystals in the amphibole mineral group) and we've even seen a few metamorphic garnets in rocks..
It's been great getting firsthand experience in identifying minerals and rock types out in the field, and I'm sure that the three of us will be well-prepared for our upcoming geology classes.
Yuem Park, Judy Pu
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