词汇 | magnetite |
释义 | BETA Examples of magnetitemagnetite isn’t in the Cambridge Dictionary yet. You can help! They also include evidence for magnetite (and/or chromite), other iron oxides and some clays. This works well, although is a little unclear when a 'black' mineral like magnetite is viewed against the black background. There are also abundant blebs of sulphides (chalcopyrite, pyrrhotite and pentlandite, inferred to have crystallized from homogeneous monosulphide globules), often enclosed by ilmenite and magnetite. The mechanisms by which magnetotactic bacteria synthesize intracellular chains of membrane-bound magnetite crystals (magnetosomes) are poorly understood. This study concentrates on the latter which contain abundant chlorite-rich layers, commonly rich in magnetite and haematite grains. The synthesis of single-domain magnetite crystals by numerous species raises the possibility that similar, conserved genes may control these biomineralization processes. The magnetite-free fraction was then passed through an isodynamic magnetic separator. The remaining magnetites lack sufficient characteristics to constrain their origin. As most of these minerals are not magnetic, it appears that the magnetite and titanomagnetite grains are imbedded in larger sediment particles containing many minerals. Ultimately, the origin of the magnetite can be resolved. The black bands contain aggregates of magnetite grains that fill similar botryoid cells with hematite one. The compositions of amphibole, plagioclase, clinopyroxene and magnetite are the actual electron microprobe analyses of the present phenocrysts. This section is overlain by a 25-m-thick, discordant, medium-grained melanocratic gabbro that grades upward into 175 m of magnetite gabbro. The groundmass is composed of fine-grained plagioclase, pyroxene, amphibole and magnetite. The main oxide minerals are magnetite, ilmenite and chromite. In the groundmass, magnetite usually occurs as euhedral grains a few to several tens of microns in diameter. They suggested that the magnetite crystals were probably produced by a biogenic process and thus interpreted these results as evidence of life. |
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