Cooled lava looks black, but why the whole volcano, even near crater, doesn't always appear black like cooled lava?
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$\begingroup$ Please edit your question and insert a pic to show what you mean. If you don't have enough rep yet to insert pictures here, put it on a generic hosting site like Imgur and insert the link here. $\endgroup$– Jan DoggenDec 14, 2015 at 9:36
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$\begingroup$ Why do you think cooled lava always looks black? There are a number of volcanic rocks hereabouts (though I'll grant that they erupted some time ago), and they run from near white (pumice) through browns and reds. $\endgroup$– jamesqfMay 3, 2017 at 4:56
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$\begingroup$ not all lava is black the mineral content of the lava has an effect. Pumice for instance can be stark white. $\endgroup$– JohnMay 4, 2017 at 16:33
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3 Answers
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The cooled lava might be covered by ashes. So depending of the amount of ashes and the wind you might have a black volcano or a gray volcano. Many volcanoes are formed by layers of lava and ash.
https://en.wikipedia.org/wiki/Volcano#/media/File:Volcano_scheme.svg
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An active volcanic crater is generally a highly toxic environment full of highly-acidic, sulphur, chloride and fluoride-rich gasses emanating from, and reacting with hot rock. Weave into the mix sudden exposure to oxygen and meteoric water (which may become reactive steam) within the rock, and you have a cocktail of extreme weathering, geochemical reaction and rock corrosion. So the original black rock doesn't stay black for long.
One bizarre and very rare exception is carbonatite volcanoes, such as occur in remote parts of the East African Rift Valley. These 'lavas' start off as white magma, and almost immediately turn black upon exposure to air.
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Not all lava is black, the mineral content and cooling speed of the lava has an effect. Cooled lava can have a variety of colors including stark white pumice. https://hvo.wr.usgs.gov/volcanowatch/archive/2000/00_10_19.html
