沙漠岩漆

沙漠岩漆（英语：Desert varnish）或岩石漆皮是在干旱环境中裸露的岩石表面上的橙黄色至黑色表层。大约一微米厚，具有纳米细的分层^[1]。岩锈和沙漠铜绿是不太常用的同意术语。

形成

沙漠岩漆只能在稳定的岩石表面形成。而且容易遭受风和水的磨损。漆皮主要由粘土颗粒以及铁和锰的氧化物组成^[2]。还含有许多微量元素和一些有机物。漆皮的颜色从棕色到黑色不等^[3]。实验研究以证明，沙漠岩漆的主要成分实际上是二氧化硅，而不是之前认为的粘土^[4] ^[5]。而且可由无机化学方法进行了复制，研究也指出，沙漠岩漆是微生物石化剂和水的指示剂。漫游者在火星上似乎也观察到沙漠岩漆^[6]。

组成

早期沙漠岩漆的物质被认为是由从它所覆盖的岩石中出来的 ^[7]。然而，它的主要部分是经由风带来的粘土^[8] 。粘土可以吸附其他物质，在沙漠的高温阳光下，这些物质和粘土加上露水会发生化学反应，而造成漆皮。 [3] 黑色沙漠岩漆的锰含量异常高。锰在地壳中相对稀有，仅占其重量的 0.12%。然而，在黑色沙漠岩漆中，锰的含量要高出 50 到 60 倍。另一种假说认为沙漠岩漆是由锰氧化微生物造成的，这些微生物在缺乏有机营养的环境中很常见。但pH 值高于 7.5 的环境就不适合富锰微生物。在这种情况下，会形成橙色漆皮，其中锰 (Mn) 含量低，但铁 (Fe) 含量高 ^[9]。 Mn/Fe 含量在沙漠岩漆的变化与潮湿和干旱气候有关^[10]。

岩石有不同的保留沙漠岩漆的能力。例如，石灰岩通常没有漆皮，因为它们的水溶性太高，漆皮易于脱落。反之不易风化的，如玄武岩、细石英岩和变质页岩等，其表面易于形成闪亮、致密和黑色的漆皮。

用途

即使有含量高的铁和锰，沙漠岩漆并无经济价值。然而，美洲原住民的岩画是用刮掉深色的漆皮来创造的。

参考文献

[1]
Krinsley, David; Dorn, Ronald; Tovey, N. K. (January 1995). "Nanometer-Scale Layering in Rock Varnish: Implications for Genesis and Paleoenvironmental Interpretation". The Journal of Geology. 103 (1): 106–113. Bibcode:1995JG....103..106K. doi:10.1086/629726. S2CID 129392419.
[2]
Perry, Randall Stewart; Adams, John B. (November 1978). "Desert varnish: evidence for cyclic deposition of manganese". Nature. 276 (5687): 489–491. Bibcode:1978Natur.276..489P. doi:10.1038/276489a0. S2CID 4318328.
[3]
Chernicoff, Stanley; Whitney, Donna (2007). Geology: An Introduction to Physical Geology (4th ed.). Pearson Prentice Hall. p. 585. ISBN 9780131751248.
[4]
Cleland, Carol E. (December 2007). "Epistemological issues in the study of microbial life: alternative terran biospheres?". Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences. 38 (4): 847–861. doi:10.1016/j.shpsc.2007.09.007. PMID 18053938.
[5]
McKie, Robie (13 April 2013). "Life on Earth... but not as we know it". The Guardian. Retrieved 2022-02-25.
[6]
Perry, Randall; Sephton, Mark (6 September 2008). "Solving the mystery of desert varnish with microscopy". Infocus (11): 62–76. doi:10.22443/rms.inf.1.36.
[7]
Blake, W. P. (1905). "Superficial blackening and discoloration of rocks especially in desert regions". Transactions of the American Institute of Mining Engineers. 35: 371–375.
[8]
Potter, Russell M.; Rossman, George R. (1977). "Desert Varnish: The Importance of Clay Minerals". Science. 196 (4297): 1446–1448. Bibcode:1977Sci...196.1446P. doi:10.1126/science.196.4297.1446. JSTOR 1744384. PMID 17776923. S2CID 31169889.
[9]
Dorn, R. I.; Oberlander, T. M. (11 September 1981). "Microbial Origin of Desert Varnish". Science. 213 (4513): 1245–1247. Bibcode:1981Sci...213.1245D. doi:10.1126/science.213.4513.1245. PMID 17744757. S2CID 39581858.
[10]
Liu, Tanzhuo; Dorn, Ronald I. (June 1996). "Understanding the Spatial Variability of Environmental Change in Drylands with Rock Varnish Microlaminations". Annals of the Association of American Geographers. 86 (2): 187–212. doi:10.1111/j.1467-8306.1996.tb01750.x.

[”Krinsley”-1] [1]
Krinsley, David; Dorn, Ronald; Tovey, N. K. (January 1995). "Nanometer-Scale Layering in Rock Varnish: Implications for Genesis and Paleoenvironmental Interpretation". The Journal of Geology. 103 (1): 106–113. Bibcode:1995JG....103..106K. doi:10.1086/629726. S2CID 129392419.

[”Perry”-2] [2]
Perry, Randall Stewart; Adams, John B. (November 1978). "Desert varnish: evidence for cyclic deposition of manganese". Nature. 276 (5687): 489–491. Bibcode:1978Natur.276..489P. doi:10.1038/276489a0. S2CID 4318328.

[”Cher”-3] [3]
Chernicoff, Stanley; Whitney, Donna (2007). Geology: An Introduction to Physical Geology (4th ed.). Pearson Prentice Hall. p. 585. ISBN 9780131751248.

[”Clela”-4] [4]
Cleland, Carol E. (December 2007). "Epistemological issues in the study of microbial life: alternative terran biospheres?". Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences. 38 (4): 847–861. doi:10.1016/j.shpsc.2007.09.007. PMID 18053938.

[”McKi”-5] [5]
McKie, Robie (13 April 2013). "Life on Earth... but not as we know it". The Guardian. Retrieved 2022-02-25.

[”-6] [6]
Perry, Randall; Sephton, Mark (6 September 2008). "Solving the mystery of desert varnish with microscopy". Infocus (11): 62–76. doi:10.22443/rms.inf.1.36.

[”Blak”-7] [7]
Blake, W. P. (1905). "Superficial blackening and discoloration of rocks especially in desert regions". Transactions of the American Institute of Mining Engineers. 35: 371–375.

[”Potte”-8] [8]
Potter, Russell M.; Rossman, George R. (1977). "Desert Varnish: The Importance of Clay Minerals". Science. 196 (4297): 1446–1448. Bibcode:1977Sci...196.1446P. doi:10.1126/science.196.4297.1446. JSTOR 1744384. PMID 17776923. S2CID 31169889.

[”Dorn”-9] [9]
Dorn, R. I.; Oberlander, T. M. (11 September 1981). "Microbial Origin of Desert Varnish". Science. 213 (4513): 1245–1247. Bibcode:1981Sci...213.1245D. doi:10.1126/science.213.4513.1245. PMID 17744757. S2CID 39581858.

[”Liu”-10] [10]
Liu, Tanzhuo; Dorn, Ronald I. (June 1996). "Understanding the Spatial Variability of Environmental Change in Drylands with Rock Varnish Microlaminations". Annals of the Association of American Geographers. 86 (2): 187–212. doi:10.1111/j.1467-8306.1996.tb01750.x.

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