It contains minerals such as pyroxene, amphibole, feldspar and 63-68 percent silica. The eruption temperature for dacitic lava is 1,500 to 1,800 degrees Fahrenheit. Dacitic to rhyolitic lava is so dangerous because it contains a high amount of crystals.Mt. Vesuvius erupts according to the Plinian model of eruption.
Foil has low emissivity, so will greatly reduce radiative heat transfer (act like insulation). It should face the side that is supposed to be cooler. But foil will not reduce conductive heat transfer, so it must be used judiciously with something that reduces conduction.
For short-term warmth, you can use foil, but it will not keep the food warm for long. Foil conducts heat, letting it pass through to outside of the food. The foil does not insulate or hold heat in without help. Use a layer of plastic wrap outside the foil or put the foil-covered food into a plastic freezer bag. They are thicker than the general storage variety of plastic bags. The plastic layer will help the foil to hold in the heat longer than a half-hour.