Seeing as it is quartz, then this is most likely a fault, or hydrothermal breccia. Quartz is extremely common so there are a few explanations, but here’s one that's reasonable given location. Quartz is soluble in water at high temperatures, like other elements and minerals, and water moves through everything in nature – even rocks. Think of table salt, when you boil water and add salt, the salt crystals dissolved faster in hot water. Upper Michigan has mining – copper and other metals – all related to the increased heat flow, therefore heated water from the Keweenawan Rift system, so that probably supplied the heat flow, which expelled hot water that allowed the mobilization of the quartz. As water moves over and over again over millions of years it will eventually cool or become super-saturated, which then precipitates the quartz, which then fills in cracks and broken fissures, encasing whatever rocks or fragments of rocks that are near – sometimes called veins. All this happened well below the surface, later it was exposed, eroded into a big chunk that got transported via water, broken up, rounded and smoothed along the way into this rock.