Dining Hall Fireplace
The Dining Hall fireplace represents a slice through a Cascade Mountain volcano. Volcanoes are formed from molten magma rising up from within the Earth’s crust.
Magma that reaches the earth’s surface can flow out as lava or can explosively erupt into clouds of ash., cinders, and hot gasses. The lava and ash pile up to form the high Cascade volcanoes such as Mount Rainier. Andesite (at the top of the fireplace) is the most common rock type in the Cascade volcanoes.
Much of the magma solidifies before it reaches the surface. This is represented by the light-colored ‘granite’ in the middle of the fireplace.
The difference in appearance between the andesite and granite is due more to texture than composition. The textures differ because the cooling rates differ. Slower cooling enables larger crystals to grow in the granite.
The ‘country rock’ rock through which the magma flows will be metamorphosed near the magma by intense heat and pressure. This is represented by the metamorphic rock in the lower part of the fireplace.