ORIGIN OF SAND COLOR AT GOLDEN AND SILVER BEACHES, RAQUETTE LAKE, NY

Golden and Silver Beaches, on the east shore of South Bay, Raquette Lake, NY (central Adirondacks) are named, respectively, for the dark yellowish-orange (10 YR 6/6) and very light gray (N8) color of their sands. Only a small, 350 m wide peninsula separates the two beaches yet their hydrologic recharge areas are strikingly different. Behind most of Golden Beach is a typical upland area underlain by glacial tills whereas the area behind Silver Beach is a low-lying bog.

Sand from both beaches comprises >96% quartz, with the remaining 2-3% K-feldspar and accessories of red garnet, ilmenite, hornblende. There are two main differences in beach sand, however. First, all of the K-feldspars at Golden Beach are pink or reddish-pink colored due to the typical presence of microscopic earthy hematite inclusions along fractures and cleavages. However, K-feldspar at Silver Beach is largely pure white. The K-feldspar at both beaches is microperthite. Secondly, about half the sand grains (quartz & K-feldspar) at Golden Beach are coated in a pale-orange colored material thought to be either amorphous iron hydroxide or goethite. None of the sand grains at Silver Beach have this coating; all are clear or gray (quartz) and pure or nearly pure white (K-feldspar).

The very light gray color of Silver Beach sand is interpreted to be the result of extensive dissolution of amorphous Fe-hydroxide, goethite, and earthy hematite. Lakeward moving water from the recharge area behind Silver Beach is interpreted to have low pH and low dissolved oxygen, thereby enhancing the solubility of amorphous Fe-hydroxide, goethite, and earthy hematite. Sand grains on Golden Beach do not experience these conditions, and thus retain their typical Adirondack coatings of iron-hydroxides.