Whether it's Nature Study or Geology, it's great having an environmental engineer for an aunt (my sister-in-law.) Not only does she know all the plants in the area, she gives you gifts like pike hammers and bedrock samples. These arrived today. She included an informational sheet as well as a pamphlet about Rhode Island bedrock, complete with a geological map!
These bedrock core samples are the metamorphic rock gneiss formed from granite, distinguishable by its distinct banding. It contains quartz (clear to gray), biotite (black banding), and feldspar (pink.) Some samples may contain flecks of pyrite (Fool's gold.)
The samples are best viewed wet. Why? Think of clear plastic wrap--when you crinkle it, it becomes white because the light is reflected by the countless surfaces it now has. The uneven rock surface (even though these are pretty smooth from the drill) is "smoothed out" by water and so the colors are more intense. This is similar to polishing rocks.
All of these pieces come from the same core sample beginning at about 40 feet deep. Each piece is marked with the depth at which that piece started. The breaks come from pockets of ground water. You can clearly see how the stone changes with depth. Yoou can't tell in these pictures but the deeper stone clearly contains a lot more feldspar than the more superficial stone, which has more biotite banding.