SpanTweenesterit

SpanTweenesterit is a rare mineral discovered in 2021 within the Green River Formation in Colorado, United States. It is named after the Spanish word "span," referring to its origin, and "tweenesterit," a playful combination of "tween" and "asterite," reflecting its unique crystal structure and intermediate properties between two other minerals, asterite and tweenite. SpanTweenesterit crystallizes in the monoclinic system and typically forms prismatic crystals with a vitreous luster. Its chemical composition is complex, consisting primarily of silicon, oxygen, and various transition metals, with a general formula of (SiO2)n(MO)m, where M represents the transition metals.

The mineral exhibits a distinctive color range, from pale yellow to deep brown, often with a slight iridescence. Its hardness on the Mohs scale is approximately 5.5, and it has a specific gravity of around 3.2. SpanTweenesterit is notable for its optical properties, displaying pleochroism and showing a strong birefringence under polarized light. It is also fluorescent, emitting a faint blue glow under ultraviolet light.

SpanTweenesterit is of interest to geologists and mineralogists due to its unique properties and the geological context in which it was found. Its discovery has contributed to the understanding of mineral formation processes in sedimentary environments, particularly within the Green River Formation, which is known for its rich fossil record and diverse mineralogy. The mineral's rarity and distinctive characteristics make it a valuable subject for further study and potential future applications in materials science.