rocks with crystals and white substance

Asked August 12, 2019, 7:28 AM EDT

Can anyone tell me what kind of rocks theses are ? I found three large rocks on our property. They have clear little crystals on outside and white crystals on inside . Thank you

Washington County Pennsylvania geology

3 Responses

Lovely rocks! The crystals are most likely quartz. The process is called secondary mineralization because silica rich waters deposited (precipitated) out the quartz, filling small openings in the country rock. The geology map for Washington County has an interesting variety of older sedimentary rocks, including coal seams. https://mrdata.usgs.gov/geology/state/fips-unit.php?code=f42125
The rocks range in age from 320 Million Years to 248 Million years. http://www.docs.dcnr.pa.gov/cs/groups/public/documents/document/dcnr_016205.pdf
The area was also heavily glaciated by the continental glaciers which carried in a lot of rocks from the north. Quartz is very durable. Given the round shape of these rocks, they may have been rolled around and carried along by ice from their original place of formation far to the north. Bet they have a great story to tell.
It's fun looking at the quartz crystals with a magnifying glass or a loupe. What a nice surprise!

Thank you Carrie for your response and information. Your right I bet they have a great story to tell.

You're welcome! Am betting your property will yield more interesting rocks. Have fun!!