Porphyry Paving Stone
What is porphyry paving stone? Porphyry is a type of volcanic igneous rock, which along with granite and other rock formations, make up approximately 95% of the world's "crust." It is different than granite and is made up of over 70% silica, about 14% alumna, 8% alkali and small percentages of iron, calcium and magnesium.
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