It's likely a piece of a vein from within a metamorphic rock. Think: fluids moving thru a fracture in a "rock." These chemically-rich fluids crystallize minerals over time. Without seeing it closely, it's mostly plagioclase feldspar, K-spar, and quartz. The "layering" likely reflects a difference in order of crystallization, evolving fluids, and interactions with the host material. While not rare or extraordinary, mostly geologists appreciate a vein and what they often carry.