球粒陨石是石陨石的一种,主要由硅酸盐组成,常见矿物为橄榄石和辉石,还有少部分铁纹石与镍纹。球粒陨石是目前发现或目击陨石最多的品种,特别是普通球粒陨石占到所收集陨石总量的80%以上,可以说在找到的100块陨石里,至少有80块是普通球粒陨石,正因如此,很多人都认为球粒陨石价值过底,球粒陨石虽然占了陨石总量的很大一部分,但是在球粒陨石中也有不少稀有球粒陨石,它们当中个别品种为科研机构带来了很大收获,这些品种有:碳质球粒陨石、顽辉球粒陨石、R型球粒陨石、K型球粒陨石。这些稀少球粒陨石品种有些只占到陨石总量的百分之零点几,珍贵程度不亚于火星陨石跟月球陨石。各品种球粒陨石外观基本没什么特别,要分辨出哪种球粒陨石,无法通过外观跟显微镜分辨出来,需要借助科学元素分析。
球粒陨石是未经过熔融的太阳系内最原始的物质,是从太阳系胚胎星云中直接凝聚出来的产物。球粒陨石的平均化学成分代表了太阳系的化学成分。球粒陨石最典型的特征是在显微镜下可看到内部含有毫米大小的硅酸盐球粒,这也是球粒陨石“球粒”得名的由来。
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鉴定一块样品是否为陨石,可以从以下几方面考虑:
1.
外表熔壳
:
陨石在陨落地面以前要穿越稠密的大气层,陨石在降落过程中与大气发生磨擦产生高温,使其表面发生熔融而形成一层薄薄的熔壳。因此,新降落的陨石表面都有一层黑色的熔壳,厚度约为1毫米。
2.
表面气印
:
另外,由于陨石与大气流之间的相互作用,陨石表面还会留下许多气印,就象手指按下的手印。
3.
内部金属
:
铁陨石和石铁陨石内部是有金属铁组成,这些铁的镍含量很高(5-10%)。球粒陨石内部也有金属颗粒,在新鲜断裂面上能看到细小的金属颗粒。
4.
磁性
:
正因为大多数陨石含有铁,所以95%的陨石都能被磁铁吸住。
5.
球粒
:
大部分陨石是球粒陨石(占总数的90%),这些陨石中有大量毫米大小的硅酸盐球体,称作球粒。在球粒陨石的新鲜断裂面上能看到圆形的球粒。
6.
比重
:
铁陨石的比重为8克/cm3,远远大于地球上一般岩石的比重。球粒陨石由于含有少量金属,其比重也较重。
To identify whether a sample is a meteorite, we can consider the following aspects:
1. External crust: Before falling to the ground, meteorites must pass through the dense atmosphere. During landing, meteorites friction with the atmosphere to produce high temperature, which melts the surface and forms a thin layer of crust. As a result, the newly landed meteorite has a black molten crust on its surface, which is about 1 mm thick.
2. Surface imprinting: In addition, due to the interaction between meteorites and atmospheric currents, there will be many imprints on the surface of meteorites, such as finger-pressed fingerprints.
3. Internal metals: Iron meteorites and iron meteorites are composed of metallic iron, which has a high nickel content (5-10%). There are also metal particles in the chondrite, and fine metal particles can be seen on the fresh fracture surface.
4. Magnetism: Because most meteorites contain iron, 95% of them can be absorbed by magnets.
5. Chondrites: Most meteorites are chondrites (90% of the total), which contain a large number of millimeter-sized silicate spheres called chondrites. Round granules can be seen on the fresh fracture surface of chondrites.
6. Specific gravity: Iron meteorite has a specific gravity of 8 g/cm3, which is much larger than that of the earth's general rocks. Because chondrites contain a small amount of metal, their proportion is also heavy.