Boulder trail – pegmatitic granite

The term “pegmatite” comes from the Greek word meaning “joined” or “fused”, referring to the large, interlocking crystals that form this rock. Pegmatitic granite forms when crystals grow to large sizes, sometimes forming crystal pockets known as druses. These pockets are like tiny hidden treasure chests.

This particular rock in the park of Tartu Nature House is special because it contains garnets. Garnets are minerals that come in various colors, including gray, pink, and dark red. Some garnet varieties are even used as gemstones. Gemstone-quality garnets can be found, for instance, in Brazil, the United States and Russia.

The garnet crystals in this erratic boulder stand out against the lighter-colored rock matrix with their darker hues.

Task: Examine this rock closer, especially its polished surface. Can you identify the garnets? These are the darker “spots” against the lighter background. Did you find them? Good! Now count how many garnet crystals are visible on the polished area. Find even the smallest ones!