AboutC. Robert Reszka, Jr. Expertise I can answer any general geology question (rocks, minerals, stratigraphy, geomorphology etc.). My expertise is in the geology of the Michigan Basin, PreCambrian, Paleozoic and Recent. I can answer questions concerning mining and petroleum exploration and production and the laws concerning those activities. I can also answer questions concerning stratigraphy of the Michigan Basin. I will also answer questions about mineral and rock collecting in the Basin. I won`t be able to answer many specific questions on hydrology, geophysics or geochemistry. I may be able to answer very general questions in those venues.
Experience I have been working for the State of Michigan for 24 years as a Geologist and a Resource Analyst. I have experience with Subsurface Geology and Petroleum Geology, mining in Michigan, and Sand Dune Mining and Protection issues.
Organizations Michigan Basin Geological Society
Publications Decade of North American Geology.
Bedrock Geology of Michigan
Question I was wondering about the origins of black sand beaches. I presume they come from the basaltic rock, but what is the actual sequence of processes that turn the rock into a black sand beach?
Answer Hi Jessica,
You are correct that the material that forms the black beaches is basalt. There are two types of black sand beaches; one where the grains are very sharp and one where the edges have been rounded over.
It's how the lava enters the water that causes the different beach types. When it flows directly into the water it is still very hot (anywhere from 750 to 1,250 degrees Celsius). Contact with the cold water shatters it into small shards. These pieces are either deposited right there, or are carried, for a short distance, along shore by the currents and then deposited. In this case the grains will be very sharp.
If a stream cuts through an older lava bed it will break down the lava into smaller pieces but these will be more rounded since the water action is bumping them around against each other and the ground. That action is like sandpaper grinding off the sharp corners. Also, if the lava pieces are transported by the ocean currents for a long distance (kilometers) any sharp edges will be worn off in the same manner.
So…you have lava, hot or otherwise, entering the water, either being beaten up by the currents or being immediately deposited to form a beach. The following websites gives you some pictures and a little more information.
