tag:blogger.com,1999:blog-8693614218792476252.post6679810085141044816..comments2024-03-09T08:06:26.066-08:00Comments on Looking For Detachment: Tremolite-Actinolite SkarnSilver Foxhttp://www.blogger.com/profile/03131032620978696727noreply@blogger.comBlogger17125tag:blogger.com,1999:blog-8693614218792476252.post-18238004129648847372013-01-16T08:01:47.970-08:002013-01-16T08:01:47.970-08:00Thanks, George! Sorry for the comment moderation; ...Thanks, George! Sorry for the comment moderation; I find it helps with spam, especially on older posts.<br /><br />I suppose there could be some hornblende present rather than just tremolite and/or actinolite, although none has been reported in the area. Mostly I'm going on crystal shape and very light greenish color in this particular sample as seen in a scope combined with sometimes being able to get the hardness, and on thin-sections and xrd from other rocks of the area. The crystal shape narrows it down to most likely an amphibole. The color makes hornblende unlikely (not enough iron). At this grain size, under a scope one should be able to flake off chlorite xtls. Epidote is more likely to be confused with idocrase (and maybe some uncommon and obscure minerals).<br /><br />In finer grained samples, one can sometimes use color, when working in a particular area where the color of certain minerals has been seen to be consistent. This method can result in incorrect IDs.<br /><br />Another very fine-grained green skarn mineral to get confused in this mess is diopside. It's only slightly harder than actinolite, but has a higher density.<br /><br />I use mindat's locality search to find the area of interest (in this case, <a href="http://www.mindat.org/loc-37241.html" rel="nofollow">here</a>). These known lists can be helpful, though don't rule out minerals not yet found or listed.<br /><br /><br />And yeah, sometimes you just call it unknown green skarn mineral!Silver Foxhttps://www.blogger.com/profile/03131032620978696727noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-55355716730365389072013-01-15T21:03:59.756-08:002013-01-15T21:03:59.756-08:00Great post! Coming from a recently graduated geolo...Great post! Coming from a recently graduated geologist who has little experience in igneous/metamorphic field work, how do you tell actinolite/tremolite from other metamorphic assemblages like hornblende, chlorite, epidote, etc when it's this fine-grained?? <br />Cheers,<br />-GeorgeGeorge Chttps://www.blogger.com/profile/04982318871108978465noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-76252829588842553952013-01-15T21:03:16.061-08:002013-01-15T21:03:16.061-08:00Great post! Coming from a recently graduated geolo...Great post! Coming from a recently graduated geologist who has little experience in igneous/metamorphic field work, how do you tell actinolite/tremolite from other metamorphic assemblages like hornblende, chlorite, epidote, etc when it's this fine-grained?? <br />Cheers,<br />-GeorgeGeorge Chttps://www.blogger.com/profile/04982318871108978465noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-51468435813833443682012-11-08T04:46:16.343-08:002012-11-08T04:46:16.343-08:00I've driven by a roof pendant area over Tioga ...I've driven by a roof pendant area over Tioga pass, never stopped to look at the non-granitic rocks, however. Always am so focused on the granite when I'm in the Sierra!Silver Foxhttps://www.blogger.com/profile/03131032620978696727noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-84251402481873143762012-11-07T12:19:05.627-08:002012-11-07T12:19:05.627-08:00roof pendant area near Mammoth - nice to read you...roof pendant area near Mammoth - nice to read your blog again, even though I'm taking time out that I probably shouldn't!coconinohttps://www.blogger.com/profile/12050625735753145388noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-41643294480294778092012-11-05T17:44:19.071-08:002012-11-05T17:44:19.071-08:00Skarn in the Sierra? I probably haven't been t...Skarn in the Sierra? I probably haven't been to the Rock Creek Trail.<br /><br />Good to hear from you! :)Silver Foxhttps://www.blogger.com/profile/03131032620978696727noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-69068775153902077402012-11-05T12:17:13.315-08:002012-11-05T12:17:13.315-08:00One of my favs is from the Sierras, along the Rock...One of my favs is from the Sierras, along the Rock Creek Trail in between Bishop and Mammoth. I miss those hikes, and could only wistfully remember them as I drove by the area on my way home this last August.Coconinohttps://www.blogger.com/profile/10975188746464205076noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-61841374843560082011-10-28T12:14:46.496-07:002011-10-28T12:14:46.496-07:00I checked out the road tags, cool! I will try to ...I checked out the road tags, cool! I will try to put them to good use. Spencer Hot Springs ... brings back memories. A friend and I camped there one winter night in the late 70s, it was gorgeous looking west over the basin in the morning, everything had a light coating of fresh snow.<br /><br />thanks again for the infoHollishttps://www.blogger.com/profile/10788942181934895493noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-11830335236737042302011-10-27T16:11:17.410-07:002011-10-27T16:11:17.410-07:00@A Good Skarn, yeah, no photos through a petrograp...@A Good Skarn, yeah, no photos through a petrographic scope, just these macros.Silver Foxhttps://www.blogger.com/profile/03131032620978696727noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-63982478208607000332011-10-27T16:10:28.202-07:002011-10-27T16:10:28.202-07:00Hollis, glad you enjoyed the read. If you drive th...Hollis, glad you enjoyed the read. If you drive through Nevada, especially on Highway 50, check my "roadside" tags, and also tags for specific roads like Highway 50, 722, 8A, 93 - and others in other states nearby. Some are in the numbers part of the tags on the sidebar (before the alphabetical tags), others are down under H for "Highway" 50, 36, etc.<br /><br />And, you can see a skarn at the Linka Mine in central Nevada if you go to Spencer Hot Springs just off Highway 50 and S.R. 367 (old 8A). Lots of garnet.Silver Foxhttps://www.blogger.com/profile/03131032620978696727noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-19998625354071755402011-10-26T17:14:37.814-07:002011-10-26T17:14:37.814-07:00No micropetrographic photos available....No micropetrographic photos available....A good skarn to youhttp://www.blogger.com/profile/09573682791396956162noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-31291289164712939732011-10-26T10:31:39.333-07:002011-10-26T10:31:39.333-07:00and ... just finished going through the Yerington ...and ... just finished going through the Yerington posts. Wow! In Accretionary Wedge 38 re "Back to School" I wrote about the value of virtual tours and online resources to amateurs. Your Yerington posts are a fantastic example, thanks for all the photos and explanations.Hollishttps://www.blogger.com/profile/10788942181934895493noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-8640898142823702502011-10-26T07:19:21.216-07:002011-10-26T07:19:21.216-07:00thanks for the info, web page. I love to plan my ...thanks for the info, web page. I love to plan my vacation travels (western US) around geology, it lends itself so well to the purpose. From road guides, the Geology Underfoot series, online resources and several classes at the U. I've learned quite a bit and it has been so enjoyable. Anyway, I usually go through the Mojave at least once a year so now I have something else to keep my eye out for while I'm there :)Hollishttps://www.blogger.com/profile/10788942181934895493noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-79766061198298034092011-10-26T06:06:09.553-07:002011-10-26T06:06:09.553-07:00Uplift and erosion will bring the originally deepe...Uplift and erosion will bring the originally deeper rocks to the surface. So there are places to see skarns, for example <a href="http://highway8a.blogspot.com/search/label/Yerington" rel="nofollow">Yerington, NV</a>. I didn't post much in the way of exoskarn photos (skarn outside the intrusive; skarn minerals formed inside, often just inside the intrusive-wallrock contact is sometimes called endoskarn).<br /><br />And it should be possible to find skarns in the Sierra Nevada, and I've seen them in quite a few places in the Mojave Desert.Silver Foxhttps://www.blogger.com/profile/03131032620978696727noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-56488458826370904182011-10-25T09:25:03.924-07:002011-10-25T09:25:03.924-07:00nice ... thanks. So are skarns only found undergr...nice ... thanks. So are skarns only found underground? maybe where the intrusion/wallrock relationship still exists? Or is it possible to go somewhere and see some? (my real question :)Hollishttps://www.blogger.com/profile/10788942181934895493noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-83596579260056300212011-10-24T18:19:30.288-07:002011-10-24T18:19:30.288-07:00Oh, sorry. Basically a skarn is a contact-metamorp...Oh, sorry. Basically a skarn is a contact-metamorphosed rock near an intrusive (can be quite a ways away), often with some metasomatism (addition of elements including, hopefully, some ore metals, often from magmatic fluids going out into the wallrock or because of related hydrothermal/mesothermal activity). Skarns are generally coarser grained than their contact-metamorphic cousins, "hornfels." Hornfelses are more often formed from fine-grained aluminosilicate rocks like shales; skarns are more often formed from calcium-magnesium rich rocks like limestones and dolomites.<br /><br /><a href="http://www.science.smith.edu/geosciences/skarn/" rel="nofollow">Skarn Web Page</a><br /><br />And, people who work with these rocks for a living argue heatedly at times about what consitutes a skarn v. hornfels v. tactite (which is which, whether skarns v. tactites are mineralized or waste rock, is the grain size significant, does there need to be addition of major and minor elements, either or both). Aarrgh. And I won't get into the skarn-tactite question here!<br /><br />Calc-silicates are minerals, and they are often the major skarn-forming minerals, but can sometimes form in other environments; these include some garnets, diopside, actinolite, tremolite, wollastonite, and others. Epidote is a calcium-bearing silicate that can form under skarn and non-skarn environments.<br /><br />I've never thought about writing about them before, could be a whole book! :)Silver Foxhttps://www.blogger.com/profile/03131032620978696727noreply@blogger.comtag:blogger.com,1999:blog-8693614218792476252.post-44939728104701097162011-10-24T15:44:53.582-07:002011-10-24T15:44:53.582-07:00I had to look up "skarn" ... first I'...I had to look up "skarn" ... first I've come across it (amateur geologist here). Simplest definition says calcium-bearing silicates (hmmm) often formed at the contact zone between granitic intrusions and carbonate rocks (now that I can relate to). What's your definition?<br /><br />NIce photos.Hollishttps://www.blogger.com/profile/10788942181934895493noreply@blogger.com