Pseudobrookite

An Unexpected Find

Starting October 10th and ending on the 11th the GEO 2500 class went on a two day geology marathon full of traveling on rough dirt roads, hiking, rock hunting and finding. We also learned about some of the major geological events that created the variety of terrain we encountered. We left Ephraim at approximately 8:45 am on the 10th and headed westward to Topaz Mountain. Roughly 116 miles later we arrived at Topaz Mountain. Almost immediately we put on our safety goggles, grabbed hammers and chisels and got to work looking for topaz. We had a variety of success finding topaz, and while looking closely at some grayish white rhyolite I stumbled upon a small black crystal called pseudobrookite. 

Pseudobrookite, which is Greek for false brookite, is a rare oxide mineral which usually forms by pneumatolytic processes or by reactions with xenoliths in titanium-rich andesite, rhyolite, basalt, according to rruff.info/doclib/hom/pseudobrookite.pdf. According to dictionary.com and merriam-webster.com, pneumatolytic means formed or forming by hot vapors or super heated liquids under pressure, the process by which rocks are altered or minerals and ores are formed by the action of vapors given off by magma.  Pseudobrookite is often found with hematite, magnetite, bixbyite, ilmenite, enstatite-ferrosilite, tridymite, quartz, sanidine and topaz. The topaz at Topaz Mountain formed in vugs located in a lava flow, and the pseudobrookite formed in the same rhyolite as the topaz in a similar process.   Pseudobrookite , which has the chemical formula Fe₂TiO₅, often has either a brownish-black, a reddish brown, or a black color. It is opaque with a metallic luster (webmineral.com).   According to http://www.mineralmarket.com/TopazMtn/topaz7.html

Pseudobrookite crystals are skinny elongate prisms with striations (look like grooves) and belong to the orthorhombic crystal system.  

The pseudobrookite was an unexpected find since we were looking for quartz and topaz. We got home late that night tired but successful in finding multiple crystals, geodes, and trilobites. The next day we left later in the day and headed to eastern Utah. We managed to find heaps of gypsum after a long day of traveling, which was very exciting. The two day road trip was a very enjoyable adventure. 

Information gathered from

rruff.info/doclib/hom/pseudobrookite.pdf, www.minweb.co.uk/oxides/pseudobrookite.htm, www.webmineral.com/data/pseudbrookite.shtml#.VEgriPnf_T8, dictionary.reference.com/browse/pneumatolytic, and www.merriam-webster.com/dictionary/pneumatolytic

http://www.mineralmarket.com/TopazMtn/topaz7.html