Octahedrite (Nantan Meteorite) 11 : 無料・フリー素材/写真
Octahedrite (Nantan Meteorite) 11 / 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 | Nantan Meteorite - octahedrite from the Asteroid Belt (2.0 centimeters across at its widest)Meteorites are rocks from space. Three basic categories exist: 1) stony meteorites; 2) iron meteorites; and 3) stony-iron meteorites. As the name suggests, iron meteorites are dominated by iron metal (elemental Fe). They also include some metallic nickel (Ni), plus minor minerals. They represent metallic core samples from differentiated asteroids/dwarf planets in the Solar System that have been disrupted by one or more large impact events.Iron meteorites come in three textural varieties: octahedrites, hexahedrites, and ataxites. Octahedrites are the most common type of Fe-Ni meteorites. The textural classification of iron meteorites has been augmented with information on trace element content.Mineralogically, all octahedrites are dominated by two minerals having very similar chemistries: kamacite (FeNi) and taenite (FeNi). Kamacite is a silvery-colored iron-nickel metal alloy rich in iron, with about 5.5 weight-percent nickel. Taenite is a silvery-colored iron-nickel metal alloy rich in nickel, with about 27-65 weight-percent nickel. Octahedrites have much more kamacite than taenite. They also contain minor amounts of troilite (FeS - iron monosulfide), silicate minerals, and others.The physical crystalline structure of octahedrites is distinctive. On cut, polished, and acid-etched surfaces (see elsewhere in this photo album), a criss-crossing pattern of silvery-gray blades is evident - this is called Widmanstätten structure. It formed when kamacite and taenite crystallized from cooling magma. The two minerals formed interlocking plates with octahedral (double pyramid) geometries.Seen here is an octahedrite called the Nantan Meteorite from northern Guangxi Province in South China. It's a group IIICD iron with ~92% Fe, ~7% Ni, and trace amounts of other minerals. The Nantan fireball was witnessed and documented by the Chinese in May or June of 1516 A.D., but samples were first recovered & recognized much later in the mid-20th century. |
| 撮影日 | 2019-09-03 16:09:16 |
| 撮影者 | James St. John |
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