Hi, folks. This is very serious. Please read.
In Sunset Magazine's April issue, page 77, they show a photo of rocks heating on a stove's burner (to be used for steaming vegetables). This is a terribly dangerous thing to show, as most people don't know what kind of rocks are safe for this kind of thing. If someone were to put rocks secured from a riverbed, or an outdoor water feature, or simply the wrong kind of rock, onto a burner -- rock they'd probably WASH first -- these rocks CAN EXPLODE.
Most rocks have a certain amount of water content, but some are like sponges, and when heated, the steam can build up and the sudden pressure can fracture the rock catastrophically, bursting into hot shrapnel that could seriously injure someone -- esp. rocks heated on a range at waist level, right about where a kid's face is. Talk about a meal blowing up in your face.
NEVER put rocks on a stove or in a campfire, unless you know what you're doing. No one should try this at home, or else it's like Da-da when he accidently ate that fish with the nitroglycerine demi glace...