MSirmon Posted March 30, 2017 Share Posted March 30, 2017 Found an interesting rock just east of Alpine TX. When cleaning it noticed an overlapping triangle pattern on the bottom. The area is cretaceous but am not sure of the formation. Any ideas? Link to comment Share on other sites More sharing options...
ynot Posted March 30, 2017 Share Posted March 30, 2017 Looks geologic. Impressions of crystals? Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
MSirmon Posted March 30, 2017 Author Share Posted March 30, 2017 Not sure about the impressions but am thinking the item is a Holaster echinoid. Probably a Holaster Simplex? Here are some reference photos Link to comment Share on other sites More sharing options...
ynot Posted March 30, 2017 Share Posted March 30, 2017 Maybe @Coco can confirm You idea of echinoid. Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
andreas Posted March 30, 2017 Share Posted March 30, 2017 Echinoid for sure. It shows the typical by cacite replaced shell. The "impressions of crystals" are outbreaks of the crystallised calcit shell material. That is very typical for echinoids all over the world. Link to comment Share on other sites More sharing options...
MSirmon Posted March 30, 2017 Author Share Posted March 30, 2017 Thank you. I was wondering about the "rock" layer on the outside and if I should try to clean off but now know to leave it alone. Link to comment Share on other sites More sharing options...
Uncle Siphuncle Posted March 30, 2017 Share Posted March 30, 2017 The pattern of triangular sections of released calcite prisms is typical of how echinoid tests weather. I see this most often in the Texas desert. Look at a geological map of the area. Holaster simplex will be restricted to areas mapped as Washita undivided or Boracho fm, Levinson member. Based on condition, I can't really make out enough diagnostic detail to key it out from photos. Grüße, Daniel A. Wöhr aus Südtexas "To the motivated go the spoils." Link to comment Share on other sites More sharing options...
Coco Posted March 30, 2017 Share Posted March 30, 2017 Hi, Perhaps we can see ambulacra (um ?) here Coco ---------------------- OUTIL POUR MESURER VOS FOSSILES : ici Ma bibliothèque PDF 1 (Poissons et sélaciens récents & fossiles) : ici Ma bibliothèque PDF 2 (Animaux vivants - sans poissons ni sélaciens) : ici Mâchoires sélaciennes récentes : ici Hétérodontiques et sélaciens : ici Oeufs sélaciens récents : ici Otolithes de poissons récents ! ici Un Greg... Link to comment Share on other sites More sharing options...
supertramp Posted March 31, 2017 Share Posted March 31, 2017 I agree with echinoid; and with regard to the “triangle pattern”, when rhombohedral calcite crystals grow interpenetrating and overlapping each other (geminated), they might resemble a tetrahedral-like structure with triangular facets https://www.google.it/search?q=calcite+geminata&rlz=1C1AKJH_enIT733IT734&espv=2&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiyvqTro4DTAhVBoBQKHXnLCiEQsAQIGQ&biw=1280&bih=863#tbm=isch&q=rombohedral+calcite+fointambleu&* ciao Link to comment Share on other sites More sharing options...
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