Mineral Report from Lechuguilla Expedition This tall room neatly illustrates several of the typical vertical zones found in the cave. One enters near the top and descends by rope about 40 ft. In this zone condensation and corrosion predominate on upward-facing surfaces. Thick layers of residual silt coat the rocks on their top surfaces. Their undersides occasionally have frostwork or calcite crystals deposited by evaporation. In this zone descending cool air (which can be felt) is mixing with warm moist air coming from below and water is condensing. Climbing further down into the lowest areas of the room, spectacular frostwork and calcite crystals cover all surfaces. Evaporation predominates. In the Southwest direction is one of the most beautiful frostwork areas I have seen in the cave, with bushes up to 4 feet high. Huge trays of scalenohedral calcite crystals cover the ceiling in this area, the largest being about 8 ft by 4 ft. At this level there are abundant calcite rafts on the floor. They are corroded, iron-stained and rusty-colored, cemented, and often covered with frostwork. These areas end in small boneyard maze. In several places air can be felt coming up from tubes that have calcite/aragonite rims. There is an UNUSUAL MINERAL in the upper part of this room. As you go over the lip of the drop (station EYWL 37) there is (on your right facing from where you came) a stalactite about 8 inches long and 1 inch in diameter. It is not straight but wavy and angles about 20 - 30 degrees towards the wall. It hangs from the lower tip of a large rock. The downward edges of the rock have calcite crystals (rhombohedrons I think). The stalactite is made of a pale translucent green mineral with a platey structure, thin (about 1 mm?) more or less parallel sheets running lengthwise. The sheets are somewhat entangled in a ropey way. The edges of the plates show flat cleavages or crystal faces. Most of the stalactite is covered with white calcite crust and rhombic crystals, but the green mineral shows clearly along one side. The calcite looks partially dissolved. There is another similar stalactite hanging nearby but further away. It is totally covered with fresh, growing (there is water on it) calcite rhombs, but I suspect the core is the green mineral. At the bottom of the drop (this is the first place you can get off the rope, though one can continue further down) a very similar stalactite was found lying on the ground. It consists of the green mineral partly covered with gauzy calcite. Very close to this point are several more of these stalactites in place at low points of large breakdown blocks. One large one (about 8 inches long) is lying under the point of a large block. It appears to have detached when the rock tip it was attached to corroded. Also, several broken pieces of the same material an inch or more long are very close to station EYWL40. These stalactites were formed in what is now (and probably was then) the upper zone described above. They are seen only at the lowest tips of large hanging rocks. This suggests that condensation moisture dissolved this mineral from the bedrock and carried it to the lowest point of the rock, where evaporation caused it to crystallize. What is it? In the hand, it feels strikingly more dense than calcite. That would suggest a barium or strontium sulfate or carbonate. Strontianite (strontium carbonate) is not reported for Lechuguilla in Cave Minerals of the World, second edition). It is described as sometimes being light green. Witherite (barium carbonate) is reported from Lechuguilla as crusts. It is unlikely, as it changes to barite if contacted by the sulfate ion. There is no gypsum nearby, but sulfate is certainly common in the cave. Barite (barium sulfate) is not reported for Lechuguilla. It is difficult so imagine how barite could form stalactites by evaporation, since barite is extremely insoluble. However, pale green to pale blue masses of it are found in Fiume-Vento Cave, Italy, associated with endellite. Could it be barite pseudomorphic after witherite? Celestite (strontium sulfate) is reported for Lechuguilla as crystals and crusts. Though usually light blue it is occasionally light green. It is less soluble than strontianite so is likely to crystallize first, but is still soluble enough to form by evaporation. I am not aware that any of these possibilities has been found in caves in stalactitic form, and the platey structure is unusual. Perhaps it is not one of the above. If the proper authorization is obtained, a sample will be taken on the next expedition, and X-ray studies should settle the question of what type of mineral this is! I will bring photos to the July 28 grotto meeting. Peter.
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