Observation and Description of Evaporite Rocks

Exercise #1: Before you come to Lab look up in any mineralogy reference text the physical and optical properties of the following minerals and make a neat table of such in your lab notebook.

Exercise #2: Examine each and every one of the following hand samples and try to identify the minerals present and observe the textural relationships. There are a few questions (in red) that you need to address in your lab write-up. 

• Sample #1333 Gypsum? Leslie salt plant, San Francisco Bay, CA. Is this pure gypsum or are there other minerals present? Sample is probably from an evaporation pan.
• Sample #1206 Native sulfur. Location unknown. Subsurface reduction of gypsum or anhydrite by anaerobic bacteria produce this native sulfur.
• Sample #1220 Gypsum. Vein filling variety known as satin spar.
• Sample #1299 Continental sabkha deposit from Rub al Khali, Saudi Arabia. What minerals are present? Look at how chaotic it is.
• Sample 1335 Halite, Leslie salt plant, San Francisco Bay, CA, This is a sample from an evaporation pan.
• Sample AZ4951A Oriented core sample (red stripe left hand side) Laminated dolomite (algal mat?) with displacive anhydrite nodules. Hypersaline lagoon depositional environment. Queen Formation (Permian), North Cowden Field, Ector Co. Texas, depth 4951 feet below drill collar.
• Sample AZ4954A Oriented core sample (red stripe left hand side) of mosaic anhydrite some times also called chicken wire texture. The nodules grew against one another displacively within the sediment. Hypersaline lagoon depositional environment. Queen Formation (Permian), North Cowden Field, Ector Co. Texas, depth 4954 feet below drill collar
• Sample H100. Laminated evaporite, Castile Fm. (Permian), Delaware Basin, New Mexico. Look closely at the laminations, the dark is clay and carbonate enriched while the white is the calcium sulfate (what type?). This is a classic sample of laminated evaporite.
• Sample #M120-11 Polyhalite
• Sample #M123-2 Sylvite and Halite from the Salado Fm. (Permian) Delaware Basin, National Potash Co., Carlsbad, New Mexico. Which mineral is which?
• Sample M159-10 Barite rose, continental sabkha, location unknown.
• Sample M164-10 Core sample, location unknown. Laminated gypsum with some iron oxide and silt. Shallow subaqueous deposit.
• Sample R4920A Nodular displacive anhydrite and dolomite deposited in a hypersaline lagoon. Queen Fm. (Permian) West Texas. Depth 4920 feet below drill collar (Oriented core sample arrow up)
• Sample R5031.2A Nodular anhydrite in bioturbated dolomite mud. Grayburg Fm. North Cowden Field, Ector Co. Texas. Oriented core sample, arrow up.
• Sample SP-750, Halite, location unknown. Hopper rafts, these floated on the surface of the pond and then broke and sank.
• Sample SP-751, You tell me what is this?
• Sample SP-752, Laminated anhydrite, Phosphoria Fm. (Permian). Core sample from a dry oil exploratory well, Sheep Mountain anticline, Graybull, Wyoming.
• Sample SP-753, Typical sabkha with anhydrite after gypsum (white) in a largely dolomite matrix. The greasy looking areas are crude oil (smell it!) Phosphoria Fm. (Permian). Core sample from a dry oil exploratory well (same as SP-752), Sheep Mountain anticline, Graybull, Wyoming.
• Sample SP-754, gypsum, svariety atin spar, location unknown.
• Sample SP-755 gypsum, variety selenite, location unknown.
• Sample SP-756, unknown what do you think it is?
• Sample WM-65 Halite casts in a laminated dolostone, probably algal mats with halite crystals growing on or within them. Basal Member of the Redwall Limestone (Mississippian) Whiterocks River, Utah.
• Sample 00-NY-1, gypsum, variety selenite, Syracuse Formation (upper Silurian), Fayetteville, New York.

Exercise #3: Examine each of the following thin sections and answer the questions.

• 795 4168 Siltstone with poikilotopic anhydrite cement. Grayburg Fm (Permian) North Cowden Field, Ector Co. Texas. Aeolian silt lens deposited in an evaporitic mudflat. Well NCU 495, depth 4168 feet below drill collar.
• 795 4269 dolomitized fusulinid wackstone with anhydrite reducing the moldic porosity after the fusulinids. Grayburg Fm (Permian) North Cowden Field, Ector Co. Texas, Well NCU 795, depth 4269 feet below drill collar
• 833 4049 dolomitized sility wackstone with anhydrite nodules. Grayburg Fm (Permian) North Cowden Field, Ector Co. Texas, Well NCU 833, depth 4049 feet below drill collar
• 833 4140 dolomitized pisolitic grainstone with anhydrite reducing the intergranular porosity. Grayburg Fm (Permian) North Cowden Field, Ector Co. Texas, Well NCU 833, depth 4140 feet below drill collar.
• 833 4153 Dolomite with pisolites (dolomitized or ghosts), anhydrite pore fillings. . Grayburg Fm (Permian) North Cowden Field, Ector Co. Texas. Well NCU 833, depth 4153 feet below drill collar.
• 833 4203 dolomite with displacive anhydrite nodule. Grayburg Fm (Permian) North Cowden Field, Ector Co. Texas..Well NCU 833, depth 4203 feet below drill collar
• SP-178 What is it? Bet you can't figure it out!
• SP-204 Dolomitized wackstone with apparent graded bedding (laminations) probably from distal turbidites note the displacive anhydrite. Location unknown.
• 39 W What can you tell me about this?  Good luck and have fun with this one!
• 795 4123 What is the diagenetic history of this one?
• 44-6167 Gypsum, variety alabaster, Pomaia, Italy. Note both the mineralogical and fluid inclusions in these gypsum crystals. What is the nature of each?
• 44-7369 Rock gypsum, Lykins Formation (Permo-Triassic) Fremont County, Colorado. Note the preferred orientations of most of the crystals. For those of you who have had metamorphic petrology do you see any similarity between the fabric of this sample and the fabric of certain metamorphic rocks? How do you explain this?
• 44-7370 Rock Anhydrite, Windsor Group (Mississippian) Hants County, Nova Scotia. This sample contains mostly anhydrite but there is also some gypsum present as veinlets. Look closely at those veinlets. Note how the gypsum crystals ore oriented long axis normal to the wall of the veinlet. What is going on with this sample? Why the two minerals? Which one is earlier in formation?
• 1205 What minerals are present here? What are the relationships between the minerals?

Email to me the answers to the questions in exercise #2 and #3.

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