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Rollstone Boulder
The Rollstone Boulder is a ten-foot-tall, 110-ton porphyritic granite glacial erratic located on a traffic island in downtown Fitchburg, Massachusetts. The boulder was exploded at its original location at the summit of Rollstone Hill and then reassembled near Fitchburg's Upper Common in 1929 from the pieces. Geology The Rollstone Boulder is a granite glacial erratic described by Peter Cristofono in his article "Minerals of Rollstone Hill" as being composed of "porphyritic Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning all ... Kinsman quartz monzonite." The phenocrysts in the boulder are plainly visible large white feldspar crystals.Cristofono, PeterMinerals of Rollstone Hill, Fitchburg, Massachusetts, USA Mindat.org. April 20, 2012. Retrieved December 17,2015. The boulder weighs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glacial Erratic
A glacial erratic is glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by glacial ice, often over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock () in Alberta. Geologists identify erratics by studying the rocks surrounding the position of the erratic and the composition of the erratic itself. Erratics are significant because: *They can be transported by glaciers, and they are thereby one of a series of indicators which mark the path of prehistoric glacier movement. Their lithographic origin can be traced to the parent bedrock, allowing for confirmation of the ice flow route. *They can be transported by ice rafting. This allows quantification of the extent of glacial flooding resulting from ice dam failure which release the waters stored in proglacial lakes such as Lake Missoula. Erratics ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
