Posted on February 8, 2024 (Updated on July 16, 2025)

could a rhyolitic magma melt a ferromagnesian mineral like olivine?

Geology & Landform

Rhyolitic Magma vs. Olivine: Can These Two Even Be Friends?

Okay, so picture this: deep down in the Earth, there’s this crazy mix of molten rock, right? It’s not all the same stuff. You’ve got magmas that are like oil and water – totally different personalities. And that brings us to a pretty cool question: Could a rhyolitic magma, which is kind of like the “fancy” magma, melt a tough guy mineral like olivine?

Rhyolite, think of it as the granite’s wild volcanic cousin. It’s packed with silica – that’s the stuff in glass – and we call it “felsic” because it’s loaded with feldspar and, well, silica. Imagine a thick, slow-moving syrup; that’s rhyolitic magma. It’s got quartz, sanidine, maybe a bit of hornblende thrown in for good measure. And get this, it erupts at relatively chill temperatures, usually around 650 to 800°C.

Now, let’s talk about olivine. This mineral is a total opposite. It’s all about iron and magnesium – a real “mafic” mineral. You find it hanging out in basalts and peridotites, rocks that come straight from the Earth’s mantle. Olivine’s a tough cookie, one of the first minerals to form when basaltic magma starts cooling down. And its melting point? A scorching 1200 to 1900°C! Talk about a temperature difference.

So, you’d think there’s no way these two could even interact, right? Rhyolite’s like, “Hey, let’s chill,” and olivine’s all, “I’m burning up here!” But here’s where it gets interesting. It’s not a simple “melt” situation.

What really happens when olivine meets rhyolite?

  • A Little Nibble: The rhyolite can actually dissolve a tiny bit of magnesium from the olivine, like maybe just a percent or two. It’s not really melting, more like the rhyolite is picking off a few atoms. Think of it as the rhyolite trying to get a little more “buff” by absorbing some magnesium.

  • More Like a Reaction: Now, if you dump a whole bunch of olivine into rhyolitic magma, things get interesting. The system tries to find a balance. Since olivine doesn’t like hanging out in silica-rich environments, it reacts. The magnesium in olivine hooks up with the silica in the rhyolite and morphs into orthopyroxene, another mineral. It’s like a chemical makeover!

  • Building a Wall: I’ve seen pictures from experiments where they put olivine in rhyolite, and the olivine grows a “reaction rim” of amphibole or pyroxene. Basically, the olivine dissolves a bit, stuff moves around, and new minerals form right on the olivine’s surface. It’s like the olivine is building a shield to protect itself.

  • Magma Mixer: This whole interaction is super important when you’re talking about magma mixing. Imagine a volcano where a shot of hot, olivine-rich magma gets injected into a chamber full of cooler, rhyolitic magma. Those olivine crystals start reacting with the rhyolite, and the rims they develop tell geologists a story about how long the mixing took and what the conditions were like. Pretty neat, huh?

    • What controls this whole interaction? A bunch of stuff:

    • Olivine’s Makeup: Is the olivine full of iron or magnesium? That changes how stable it is in the rhyolite.
    • Rhyolite’s Recipe: How much magnesium and silica is already in the rhyolite? That matters too.
    • Temperature: Crank up the heat, and things react faster.
    • Pressure: Yep, pressure plays a role in which minerals are stable.
    • Water: Water in the magma can really stir things up, changing how minerals behave.
    • Time: The longer the olivine sits in the rhyolite, the more it’s going to react.

    Bowen’s Reaction Series: The Big Picture

    This whole olivine-rhyolite thing is a great example of Bowen’s Reaction Series. It’s basically a guide to how minerals form as magma cools. Olivine is a high-temperature mineral, so it’s totally out of its element in the low-temperature, silica-rich world of rhyolite. That’s why it reacts and tries to find a more comfortable state.

    The Bottom Line

    So, can rhyolitic magma melt olivine? Not really. It’s more like a chemical handshake, a bit of dissolving, and a whole lot of reacting. The olivine changes, the rhyolite might change a little, and you end up with a geological story etched in the rocks. And that, my friends, is why geology is so darn cool.