Pumice and Scoria for Dummies

Pumice (left) and scoria (right)

If you weren't aware of it already, you may have noticed that we regularly check all of our posts to avoid the specter of dead links. Although certain other sites aren't particularly squeamish about sending people to "404" messages, we'd rather that people be able to find the originals of the posts we lampoon. Sometimes the hapless intern assigned to perform these checks learns that the host site has deleted the content or redirected the links (see the bold red links scattered through the lists sorted by name), but the best is when we find that it's been  rewritten. That's especially delicious when the rewrite job is no better than the original; like Blake Flournoy and their Sciencing.com attempt to tell us, "What Is the Difference Between Pumice and Scoria?"

We had to laugh this time, because Flournoy was attempting to correct a steaming pile of misinformation published by one of our favorite DotDs, the one and only Joan Whetzel. Joan's version of this "answer" was riddled with inaccuracies, so it makes sense that Leaf Group would want to correct it. What doesn't make sense, however, is that Flournoy's version isn't much of an improvement. Oh, they avoided the discussion of chemistry that made Whetzel's answer so bogus, but – like Joan before them – Blake missed the point. Here's the critical line in the definition of scoria from the Dictionary of Geological Terms:

"[Scoria is] ...characterized by marked vesicularity, dark color, heaviness, and a texture that is partly glassy and partly crystalline..."

Flournoy apparently really wants their readers to know that, "It should also be noted that pumice is technically a glass, rather than a rock... Technically, pumice is a glass rather than a proper stone..." ...which is utter bull, since pumice is indeed a rock and no geologist on earth knows what a "proper stone" might be! But that does raise the question: what, then, is scoria? what is pumice? if you had a sample of each in your hand, how would you know the difference? The differences are simple and straightforward:

• The two generally have different chemistry: scoria is relatively rich in iron and magnesium (basaltic composition), while pumice has more aluminum and silicon (rhyolitic composition). None of those bold words appears in Blake's article.
• Pumice is entirely glassy, scoria is partially or entirely crystalline. Although Blake makes much of the glassy nature of pumice, nowhere does he mention the presence of visible mineral grains in scoria.
• Blake nibbles around the edges of the physical properties of the two without comparing them: pumice is light in color, scoria is darker; the density of pumice is so low it will float until saturated, while scoria is much denser.

We had a giggle at Flournoy's ham-handed attempts to "[find] new ways to connect students to [geology]," which include such semi-scientific notions as,

• "Created by the cooling of molten lava and stone particles, igneous rocks..." – WTF are "stone particles"? Aren't those some of what makes up clastic sedimentary rocks?
• "Igneous extrusive rock cools quickly because of the difference in pressure between the surface of the planet and the planet's interior..." – Chances are pretty good the difference in temperature has quite a bit to do with it, Blake!
• "[Scoria] contrasts with pumice stone, which holds slightly different properties" – Geologists think the differences are pretty darned significant, Blake.

There's more, but we've run out of time... so without further ado, the Antisocial Network staff geologist hereby awards to Flournoy the singular honor of Dumbass of the Day. Wear it well, Blake.

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