texasrockstar
off to a rocking start
Member since January 2012
Posts: 17
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Post by texasrockstar on Apr 25, 2012 1:10:01 GMT -5
Alright... I'm amending this thread now that I've sliced these guys open with my new saw. The little one Im assuming is tigers eye?. The piece of Foss Wood is off a big chunk i have and just happened to be in the picture so no need to id that. The main things I'm wondering about are the ones on the left that I'm assuming is some sort of agate and the ones on the upper right which may be some sort of flint? The area where I found it is mostly all grey and brown flint. That's why I was incredible surprised to find that little "Tigers Eye?" piece there one day. FYI If it helps they're a little bit "cloudy" due to saw abrasion. This should fix in the tumbler right? I just bought a $30 tile saw on CL so I'm new to the whole slicing thing. imgur.com/nt7XX,X3cIh,G85Qe,ncKH7 [EDIT: I replaced the pic with a link. It was so big it was getting unbearable for me to read the post lol. Thanks, Jeff
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Post by roy on Apr 25, 2012 9:10:35 GMT -5
welcome jeff
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sheltie
freely admits to licking rocks
Member since January 2012
Posts: 982
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Post by sheltie on Apr 25, 2012 9:21:06 GMT -5
Living here in central Texas is like living in a desert with regard to interesting rocks. The rock in the forefront looks like jasper and the others are too hard to tell. Here in Georgetown area, I've only found flint and RARELY jasper with a few small undistinguished agates thrown in. For most anything worth looking for, you have to head west and southwest from here.
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texasrockstar
off to a rocking start
Member since January 2012
Posts: 17
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Post by texasrockstar on May 2, 2012 17:39:42 GMT -5
Figured I would bump this thread once for the revision... Btw is the pic too big?
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Sabre52
Cave Dweller
Me and my gal, Rosie
Member since August 2005
Posts: 20,466
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Post by Sabre52 on May 2, 2012 18:21:01 GMT -5
Don't want to make light of your finds but as a central Texas resident myself I'd say everything you've pictured is in the flint/chert group. Like Sheltie says, we're pretty much in a limestone desert here with few good quartz minerals. While most central Texas flint is brown, gray, or black tones, I often find reds, golds, yellows, purples etc. Real geologists often say true flint is in chalk deposits so our limestone rocks only yield chert but they are all the same chemically. Round here, we call the nodular forms flint and the vein stuff chert but again, pretty much all the same. There is good jasper and agate southeast of San Antonio, especially down around Live Oak County but here in Kerr and Gillespie Counties, pretty much all flint/chert. We do have some odd pseudomorphs that appear to be fossil replacements that have bluish material that for all intents and purposes is chalcedony but again I guess it's actually translucent flint. Tiger-eye, so far as I know, occurs only in Africa, Australia, Arizona, and California in various forms. None in Texas and I don't think we have the right geology for it either......Mel
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texasrockstar
off to a rocking start
Member since January 2012
Posts: 17
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Post by texasrockstar on May 2, 2012 18:53:08 GMT -5
Hey Mel, I could see the rest (except the foss. wood) being flint except for the one I wrongly assumed was Tigers Eye. It didnt seem to fracture choncoidally like most flint rocks Ive found and the colors are very vivid (way more so that the picture shows). Is there any way its some type of agate or jasper? Ive never seen flint/chert in my area that not grey or brown. Also, the one on the left I found at Lake Travis/Mount Bonell which is known for mexican agate. Does that make a difference or do you still think its flint/chert?
BTW...Thats always annoyed me too how flint also goes by chert, and I cant really tell the difference. Also, arnt flint and chalcedony both formed by silica? If so I would have to believe some of the people that claim to have found agates around here. I'm more of a fossil guy so Im just learning about ID'ing rocks. Thanks for your help! Jeff
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Sabre52
Cave Dweller
Me and my gal, Rosie
Member since August 2005
Posts: 20,466
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Post by Sabre52 on May 2, 2012 19:20:47 GMT -5
Howdy Jeff, Yep, I find a piece of silicified wood here on the ranch every now and then. Gets really abundant down south and east of San Antonio but pretty rare here. Agate, jasper, flint, chalcedony and chert are all basically microcrystalline quartz and are alike chemically ( though they may contain inclusions of other minerals giving them various colors and patterns and jasper is more fibrous in nature.). Most geologists associate true jasper and agate with igneous deposits where the silica comes from sources associate with vulcanism. Though there are sedimentary agates like Dryheads and Fairburns etc. Common names lend enormous confusion to classifying these materials. Flint and chert are from oceanic sedimentary deposits where the silica comes from organic sources like diatom and radiolarian skeletons, sponge spicules etc.. I would be very surprised to find any Mexican agates around Lake Travis as all those come from the flows of the ancient rivers that drained SW Texas and adjacent Mexico. These Rio Grande Gravel deposits run mainly from south of Uvalde south and east towards Falcon Lake and it's surrounding area. Technically, these are known as Rio grande Agate as Mexican Agate should be used for those materials that actually come from Mexico to avoid confusion. *L* Tiger Eye and it's relatives have included fibrous crocidolite or asbestos creating a flash or chatoyant effect when viewed at various light angles. Usually not associated with sedimentary rocks like we have here in central Texas. We've had long discussions here on classifying microcrystalline quartz in the past and there are a lot of opinions but basically if you get into the chemistry they are all pretty much the same and differ mainly n common names assigned to them based on numerous criteria ( ie. Colors, patterns, banding, origin, claim name, general morphology etc.) It's all pretty mixed up and you'll find a lot of different opinions on the subject....Mel
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