Pseudobrookite

Less widely known for Thomas Range, but equally impressive, are the pseudobrookite specimens from this locality. This specimen features a grey rhyolite host rock with several vugs lined with sparkling colourless quartz crystals that surround striking "star"-like sprays of thin, brownish-black pseudobrookite needles. These sharp, radiating crystals contrast beautifully with the pale quartz, making for a well-balanced example. I also see what looks like a hematite blade near the bottom. Pseudobrookite is an uncommon titanium-iron oxide mineral, and the Thomas Range material is considered among the world’s best.

The Thomas Range is a north-south trending mountain chain in western central Utah. The range consists of Miocene-aged rhyolite domes (22–6 million years old) formed through explosive, highly felsic volcanism. This geological history has resulted in a rich diversity of minerals. Although mining for uranium and other elements has been attempted, commercial success was limited, and the area has instead gained fame among mineral collectors. The volcanic rocks—mostly rhyolite and andesite in the form of flows and tuffs—are fine-grained, light-coloured, and often vuggy, providing ideal conditions for crystal formation. Topaz Mountain lies at the southern end of the range, and Spor Mountain, noted for beryllium minerals, lies just to the southwest.

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This specimen comes from the collection of Dr. Peter Tarassoff, a prominent figure in mineralogy, particularly known for his work at Mont Saint-Hilaire (MSH). His diligent collecting and examination efforts have led him to be the first to identify at least 35 species and discover 12 new species, not only at MSH but also at other alkaline localities. Dubbed the "Dean" of Mont Saint-Hilaire collectors, Peter was honoured with the naming of the new species petarasite in 1980. He has authored or co-authored numerous mineralogical articles and has been a member of the Mineralogical Association of Canada since 1964. Additionally, Peter has volunteered at the Redpath Museum for the past 21 years, where he was formally appointed the Honorary Curator of Mineralogy. In recognition of his significant contributions to mineralogy, Peter was awarded the 2017 Pinch Medal.