Carbonatite (Chilwa Alkaline Province, Early Cretaceous, 126 Ma; Chilwa Island, Lake Chilwa, Malawi, southeastern Africa) : 無料・フリー素材/写真
Carbonatite (Chilwa Alkaline Province, Early Cretaceous, 126 Ma; Chilwa Island, Lake Chilwa, Malawi, southeastern Africa) / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Carbonatite from the Cretaceous of Malawi, Africa. (7.4 centimeters across at its widest)Carbonatites are rare igneous rocks - they are composed of carbonate minerals, typically calcite (CaCO3 - calcium carbonate). Carbonatites are essentially igneous limestones.The four categories of carbonatites are:1) calciocarbonatite (calcite-dominated)2) magnesiocarbonatite (dolomite-dominated)3) ferrocarbonatite (siderite-dominated)4) natrocarbonatite (sodium carbonate-dominated)Calciocarbonatites are the most common type, whereas natrocarbonatites are extremely rare, which are only found at Ol Doinyo Lengai Volcano in eastern Africa.The carbonatite seen here is from the Early Cretaceous-aged Chilwa Alkaline Province, an igneous complex consisting of intrusive igneous rocks (alkali granites, syenites, alkaline syenites, nephilinites, and carbonatites) and extrusive igneous rocks (lavas - basanites, phonolites). The complex was intruded in phases throughout the Early Cretaceous, from about 111 to 138 million years ago.The rock doesn't readily bubble in acid. When powdered, it mildly effervesces in acid - I suspect it is dolomitic or ankeritic (?).Geologic unit & age: Chilwa Alkaline Province, late Barremian Stage, mid-Early Creatceous, 126 Ma (= absolute date of Chilwa Island carbonatite)Locality: Chilwa Island, western Lake Chilwa, southeastern Malawi, southeastern Africa |
| 撮影日 | 2014-08-03 19:56:14 |
| 撮影者 | James St. John |
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