Mt. Oldoinyo Lengai (Ol Doinyo Lengai), Arusha Region, Tanzania

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Apophyllite-(KF) : KCa₄[(F,OH)\|Si₈O₂₀] · 8H₂O
	Mt. Oldoinyo Lengai (Ol Doinyo Lengai), Arusha Region, Tanzania FOV=3.5 mm. Photo by Stephan Wolfsried; analysis by Guenter Blass (by EDS: 63.8% Si, 6.9% K, 29.2% Ca). Sample collected by Hans Eugster. This photo is of a mass of apophyllite inside a vesicle in a strongly peralkaline nephelinite lava, collected shortly after an explosive eruption in 1966. This sample formed part of a suite of specimens ...
© Stephan Wolfsried	Photo ID: 234295 View Count: 20
Combeite : Na₂Ca₂Si₃O₉, Nepheline : (Na,K)[AlSiO₄], Aegirine : NaFe³⁺[Si₂O₆], Sodalite : Na₈[Cl₂\|Al₆Si₆O₂₄]
	Mt. Oldoinyo Lengai (Ol Doinyo Lengai), Arusha Region, Tanzania Combeite (large colorless with inclusions), aegirine (green, acicular), nepheline (colorless, rectangular), and sodalite (colorless modified cubes, below largest combeite). Sample collected by Hans Eugster; sample in possession of T. Peterson. Plane polarized light: see accompanying photo with crossed polars.
© Tony Peterson	Photo ID: 46535 View Count: 545
Combeite : Na₂Ca₂Si₃O₉, Aegirine : NaFe³⁺[Si₂O₆], Nepheline : (Na,K)[AlSiO₄]
	Mt. Oldoinyo Lengai (Ol Doinyo Lengai), Arusha Region, Tanzania Photomicrograph of combeite (large crystal), aegirine (green), and nepheline (colorless, rectangular) in strongly peralkaline nephelinite lava from Oldoinyo Lengai (plane polarized light). Sample collected by Hans Eugster; sample in possession of T. Peterson.
© Tony Peterson	Photo ID: 46532 View Count: 337
Gregoryite : (Na₂,K₂,Ca)CO₃, Nyerereite : Na₂Ca(CO₃)₂
	Mt. Oldoinyo Lengai (Ol Doinyo Lengai), Arusha Region, Tanzania Photomicrograph of a thin section of natrocarbonatite lava, here dominated by rounded gregoryite with tabular nyerereite. See additional photo with crossed polars. Collection and photo, T. Peterson (lava collected by Charles Milton). The blue patches are stained epoxy.
© Tony Peterson	Photo ID: 104685 View Count: 524
Nyerereite : Na₂Ca(CO₃)₂
	Mt. Oldoinyo Lengai (Ol Doinyo Lengai), Arusha Region, Tanzania Nyerereite as rounded, pseudohexagonal phenocrystals in lava from the type locality the Oldoinyo Lengai vulcano, Arusha, Tanzania. The crystal form is visible behind the protective layer of vulcanic "glass". Specimen and photo: Knut Eldjarn.
© Knut Eldjarn	Photo ID: 147573 View Count: 274
Nyerereite : Na₂Ca(CO₃)₂
	Mt. Oldoinyo Lengai (Ol Doinyo Lengai), Arusha Region, Tanzania Photomicrograph of a thin section of natrocarbonatite lava. Nyerereite occurs as the central, rectangular crystals and also the long acicular crystals in the groundmass. The rounded colorless crystals are gregoryite and the opaques are alabandite. Two crossed-polars photo also uploaded. Collection and photo, T. Peterson (lava collected by Charles ...
© Tony Peterson	Photo ID: 104681 View Count: 451
Phillipsite-K : (K,Na,Ca_0.5,Ba_0.5)_4-7[Al_4-7Si_12-9O₃₂] ^. 12H₂O
	Mt. Oldoinyo Lengai (Ol Doinyo Lengai), Arusha Region, Tanzania FOV=1.5 mm. Photo by Stephan Wolfsried; analysis by Guenter Blass (by EDS: 5.5% Na, 12.8% K, 16.6% Al, 64.1% Si, 0.5% Fe, 0.5% Ti). Sample collected by Hans Eugster. This photo is of a vesicle lined with phillipsite crystals in a strongly peralkaline nephelinite lava, collected shortly after an explosive eruption in 1966. This sample formed ...
© Stephan Wolfsried	Photo ID: 233970 View Count: 73
Rhodesite : KHCa₂Si₈O₁₉·5H₂O
	Mt. Oldoinyo Lengai (Ol Doinyo Lengai), Arusha Region, Tanzania FOV=3 mm. Photo by Stephan Wolfsried; analysis by Guenter Blass (by EDS: 19.7% Ca, 9.3% K, 0.6% Al, 70.4% Si). Identity confirmed by XRD. Sample collected by Hans Eugster. This photo is of a vesicle containing a rhodesite tuft in a strongly peralkaline nephelinite lava, collected shortly after an explosive eruption in 1966. This sample formed ...
© Stephan Wolfsried	Photo ID: 234071 View Count: 73