tag:blogger.com,1999:blog-1228690739485734684.post7620809343076191196..comments2024-03-28T14:00:12.372+00:00Comments on Stonehenge and the Ice Age: Where did the Sleek Stone giant erratics come from?BRIAN JOHNhttp://www.blogger.com/profile/00413447032454568083noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-1228690739485734684.post-55557259617060856012015-03-24T09:45:34.245+00:002015-03-24T09:45:34.245+00:00I see now that the crystals or megacrysts are &quo...I see now that the crystals or megacrysts are "complete" and clearly defined in the porphyritic rocks, and are set in a darker matrix. In contrast, the crystal forms in the second photo -- the one you refer to as a coarse-grained sandstone -- are much more fuzzy or broken, and the matrix seems to consist of similar material -- presumably bits and pieces of quartz? The question is this -- could those sandstones have come from Ramsey as well? The island is very complex geologically, but there are sediments there, mixed in with all those volcanics. Richard knows the island as well as anybody else.....if not better!BRIAN JOHNhttps://www.blogger.com/profile/00413447032454568083noreply@blogger.comtag:blogger.com,1999:blog-1228690739485734684.post-8417589933965273652015-03-23T19:34:59.243+00:002015-03-23T19:34:59.243+00:00Thanks again -- excellent. I'll try and take ...Thanks again -- excellent. I'll try and take another trip down there to collect some samples.BRIAN JOHNhttps://www.blogger.com/profile/00413447032454568083noreply@blogger.comtag:blogger.com,1999:blog-1228690739485734684.post-79878178286944380762015-03-23T17:53:47.506+00:002015-03-23T17:53:47.506+00:00The feldspar megacrysts are euhedral
And zoned. Th...The feldspar megacrysts are euhedral<br />And zoned. There is no other large crystal/clast.<br />Two probably has large feldspars but also has irregular clasts plus at least two of your porphyries have turned out to be cg arkosic sandstones and I am guessing this is another BUT seeing the real rock is a first step.<br />MMyris of Alexandrianoreply@blogger.comtag:blogger.com,1999:blog-1228690739485734684.post-81072932898493125962015-03-23T16:45:04.016+00:002015-03-23T16:45:04.016+00:00Thanks Myris -- very useful, even if everything is...Thanks Myris -- very useful, even if everything is speculation until such time as it isn't. Can you please educate us as to why you reckon pics 1 and 3 are porphyry whereas 2 is a coarse sandstone? We are all on a steep learning curve here, and specialist education is always welcome!BRIAN JOHNhttps://www.blogger.com/profile/00413447032454568083noreply@blogger.comtag:blogger.com,1999:blog-1228690739485734684.post-56417101182695539642015-03-23T14:04:36.659+00:002015-03-23T14:04:36.659+00:00Its a mugs game.
1 porphyry certainly zoned altere...Its a mugs game.<br />1 porphyry certainly zoned altered feldspar megacrysts<br />2 Arkosic cg sst<br />3Porphyry see 1.<br />4 Scottish granite/granodiorite<br />5 Only Sublime Apollo Knows.<br />M<br />Send freshly broken samples.Myris Of Alexandrianoreply@blogger.com