This is located at the Lake Elmo Park Reserve near the town of Lake Elmo, MN. Vehicle permits are required. Park hours are 6:00 a.m. to 10:00 p.m. everyday (Sunday through Saturday).
As part of granite rock, quartz is the primary mineral in granite’s composition next to Feldspar. Quartz forms from molten magma that is slowly cooled beneath the earth’s surface. Then, as the granite rock becomes uplifted through glacial action, the overlying rocks erode to expose the quartz rock at the earth’s surface.
At this location, this large piece of quartz stands out amongst the other primarily sedimentary rocks in this area. It was most likely transported from a far away place north of here, contained within glacial till. Glaciers advanced north to south over 12,000 years ago, and as they pushed forward and then slowly receded, they dropped off erratics, such as this piece of quartz.
Compared to other minerals, quartz has the lowest potential for weathering, so it is very common as a residual rock in stream sediments or residual soils. There are many varieties of quartz rocks ranging from rare colorless crystal-shaped prisms, viewed as a gem, to more opaque varieties. The quartz at this location is milky quartz which is the most common type of quartz. The white color is caused by minute fluid inclusions of gas, liquid, or both which become trapped during crystal formation. It is of little value for quality gemstone application.
To receive credit for this earthcache, please message me with the answers to these questions:
- Describe the color of this quartz rock. Would it be used for quality gemstones? Why or why not?
- Estimate the diameter of this quartz rock.
- What geological processes formed and transported this rock to this location?