Melted Rock for Dummies

Uhhhh, no, Linda, rocks don't melt...

Every once in a while one of our researchers runs across a freelancer's post that is so downright stupid that the poor drone is left gasping for air. Today's post is precisely that: a pile of scientific ignorance so filled with misinformation and misstatements that it could only come from a journalism major writing at eHow.com... and by golly, that's exactly what our staffer turned up this time. Picture, if you will, some fine arts student stuck in Rocks for Jocks to complete that 3-semester hour science elective who needs to know "What Factors Affect the Melting Temperature of Rock?" Heaven forbid he or she should accidentally happen on the rubbish published by freelancer Linda Harris at eHow.com and moved by Leaf Group to Sciencing.com.

Heaven forbid, because Harris opens by "informing" her readers that

"Although the phrase 'melted rock' is used, technically the rock doesn’t melt at all. Instead the particles that form the rock change, causing crystals. Rocks that have melted are called metamorphic rocks. Metamorphic rocks are known as magma when they are under Earth's surface, and lava when a volcano expels them."

The only thing Linda got right in her introductory paragraph is that melted rock is known as magma in the subsurface and lava on the surface. Everything else? Flat. Out. Wrong. Rock melts all the time – igneous rocks are all crystallized from melted rock. Metamorphic rocks are something completely different!

But let's not belabor Linda's scientific illiteracy... let's see what else she has to say. It appears that Harris stumbled upon some useful references, which informed her that "Rock melts [at] temperatures between 572 degrees Fahrenheit and 1,292 degrees Fahrenheit" "The higher the water content of the rocks, the lower the melting point..." ...while on the other hand she harvested some utter crap by misreading her references; crap like

• "Certain types of rock, such as basalts, must be exposed to high temperatures for a very long time before they start to melt."
• "A great deal of pressure is inside Earth, which causes heat. Imagine rubbing your hands together very hard; this pressure causes heat. Something like this happens -- on a much-larger scale -- under Earth's surface, which is why magma exists in Earth’s core."

We really don't want to have to deal with this kind of crap, but: we have no idea where she got the ridiculous notion that basalt needs more time to melt than some other rocks. Anyone who remembers elementary physics (not in the curriculum at most J-schools) knows that a melting point is a melting point. Sure, there's a little slop for latent heat of crystallization, but "a very long time"? Give us a break!

Harris' finest moment comes early on, however, when chatting about the water content of "rocks":

"...water mixes with the rock particles and speeds up the formation of crystals."

Ummm, beg pardon, Linda, but weren't you supposed to writing about melting, not freezing? Sure you were... not to mention the abject stupidity of that "rock particles" bull. No, Harris stumbled across an article on the crystallization temperatures of melts of different compositions (though it's not in her "references") and conflated that with metamorphism; along the way getting about half of what she said backward. What a dumbass, a Dumbass of the Day!

Oh, and Linda? there's no magma in Earth's core: it's mostly iron with some nickel for good measure. All the magma is in the lithosphere. Idiot.

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