This is a fine specimen of a California pseudomorph that is very rare and difficult to find in good specimens on the market now. What strikes you first about the specimen is that when you pick it up, it weighs almost nothing - almost like Styrofoam! Mirabilite, also known as "Glauber's salt," is a hydrous sodium sulfate. Here, it has been replaced by thenardite, a mineral that forms from the evaporation of bodies of water (especially found in playa lakes). The super-sharp hoppered forms of the mirabilite have been perfectly preserved; they look like modern art.Ex. Jim Minette Collection.From Rock Currier: "Those specimens showing the long prismatic mirabilite were collected by Jim Minette from the settling ponds out west of the big open pit mine. They take the mud slurry from the million gallon plus round dissolving tanks that are used at the refinery to dissolve the crude borax ore and run it into the settling ponds to settle out the fine mud/clay particles. Any water that is not evaporated naturally, they run back through the system. Sometimes the water in these ponds is saturated with sulfate and under the right temperature conditions, usually early in the morning, crystals of mirabilite grow rapidly in the ponds, and in the ones that Jim collated the mirabilite grew in prismatic crystals. Some of these had a little "iron" in them, so when the crystals dried out they were pink in color. Jim would put them on the bank of the pond and when they dried enough he would take them home and spray them with Krylon plastic to preserve them."This Photo was Mindat.org Photo of the Day - 7th Oct 2009