Creek Bed Possibilities Realized

The previous post displayed one possible glacial rock found in the creek bed for crafting into some rock decor item; specifically coasters. Because this rock is exposed to the elements within the soil, the outside reveals significant weathering. By weathering we mean minerals in the rock will alter and break down due to chemical reactions with the surrounding environment. There is also physical weathering that occurs due to breaking up of minerals by abrasion and/or freeze/thaw behaviors. This rock contains different minerals with differing degrees of weathering, thus exhibits a very rough and irregular surface, which is revealed on the outside edge of the coaster. In contrast, rocks found on the lake shore will have smooth surfaces due to the wave tumbling actions. They have less exposure to “weathering conditions” and spend most of their time under water reducing the amount of potential chemical weathering. For the case of this gneiss found in the creek bed,the garnet crystals will weather more quickly than quartz.

The coaster surface is a 2-dimensional cut through the rock showing the layers of garnet (dark red), quartz (milky white), biotite mica (black), and other minerals. This cut is approximately from left to right in the rock image.

Large Gneiss With Significant Weathering

Coaster (7” x 5”)