Shales like the Marcellus Shale are usually deposited out in quiet, relatively deep water. Closer to shorelines, and on shorelines, you get coarser sediments including sand. Sands on beaches tend to get washed and winnowed by wave action, so unless there is some source for other materials than the quartz grains in the sand, you can end up with a rock, sandstone, that’s really pretty pure quartz, silicon dioxide.
|Photo by Kevinaj, public domain via Wikipedia.|
Caudy’s Castle (Oriskany Sandstone), West Virginia
The historical name for these glass sands was Oriskany, but that’s really a large group of related, similar, but not necessarily exactly equivalent sandstones. The glass sand miners didn’t care of course – they just went after the sand that gave them the best glass. These sandstones in the subsurface can also serve as excellent reservoirs for natural gas.
—Richard I. Gibson
Photo by Kevinaj, public domain via Wikipedia. Caudy’s Castle (Oriskany Sandstone), West Virginia.