Figure 7. Lucerne Granite, in bedrock outcrop along Route 1A in Lucerne, Maine. It is characterized by large feldspar grains, although a range of smaller grains is also present. As with all true granites, the Lucerne Granite is composed of three main minerals - two types of feldspar and quartz - in roughly equal proportions. The two types of feldspar can be distinguished readily under a petrographic microscope or by X-ray or chemical analysis, but in the field it may be difficult to tell them apart. In the Lucerne Granite, the sodium-rich feldspar (plagioclase) is generally more milky white, and the potassium-rich feldspar (alkali feldspar) is generally grayish-white and slightly translucent. The quartz is a decidedly darker gray color, and more translucent like stained glass. Quartz of this color is called smoky quartz. A fourth mineral, the black mica called biotite, makes up the remaining several percent of the rock. For more details visit the Maine Geological Survey's Lucerne Granite web site (Photo by Henry Berry).
Last updated on November 20, 2012