Sand Beach is one of the most popular locations for tourists in Acadia National Park. It’s one of the only sand beaches on Mount Desert Island. The composition of the sand here is primarily shell fragments of urchins, barnacles, periwinkles, and mussels (Acadia National Park n.d.) with minor amounts of quartz.
Sand Beach
Mount Desert Island
Sand Beach is marked in blue.
Latitude: 44°19'45.30"N
Longitude: 68°10'55.85"W
The Cadillac Mountain Granite is about 420 million years old, and makes up the rocks on the west side of Sand Beach (or the right hand side if you’re looking out over the water). This rock is labeled Dcg on the bedrock geology map of Maine. Granite is an igneous intrusive rock. This is the same granite found on Cadillac Mountain. It is a pink color due to the abundance of potassium feldspar. The other two main minerals in this rock are quartz, and hornblende. Cadillac Mountain Granite is usually a dark brown-grey color at the surface due to weathering from exposure--wind, rain and ice. Eventually this weathered surface will turn into a light gray-brown. However, the pink colour of the rock can be clearly seen at other popular sites like the Blue Hill Overlook at the top of Cadillac Mountain where the surface is fresher. Another cool mineral that can be found at Sand Beach is Epidote. The epidote at this field site is a light green mineral with small crystals that are usually difficult to see without a magnifying glass. It can be found along some of the fractures in the Cadillac Mountain Granite, and also on the other side of the beach in some of the boulders and on the bedrock.
Small scale view of the Cadillac Mountain Granite
COA student Emily Kaplan standing next to the shatterzone on the east side of the beach. 2015
Geology of MDI student standing in front of the Shatter Zone
Close up of the Shatter Zone.
This rock is about the same age as the Cadillac Mountain Granite - 420 million years old
Zoomed in view of the Shatter Zone
The Shatter Zone (labeled Dsz on the geologic map of Maine) makes up the rocks on the east side of the beach. The rock that makes up this formation has lots of smaller chunks of rock inside of it. This is because about 420 million years ago magma from deep inside the earth’s mantle flowed upwards towards the Earth’s surface and forcefully intruded the earth’s crust as the collapsed super volcano (caldera) resurged. The magma resurged and exploded upwards with such force that it shattered the country rock around the intrusion into smaller pieces, and then cooled around them to create this strange looking rock (Marvinney, 2010). This means that the rocks inside of the shatter zone matrix are different depending on where you are on MDI. Most of the magma that resurged cooled to become the Cadillac Mountain Granite and Somesville Granite with minor amounts of gabbro and diorite (Marvinney, 2010). The Shatterzone can be found all over MDI surrounding the Cadillac Mountain Granite which makes up most of the island (Marvinney, 2010).
On Sand Beach the Shatter Zone contains Bar Harbor Formation and basalt inclusions. The Bar Harbor Formation is a meta-sedimentary rock that exists outside of the Shatter zone in other places around the island. The matrix around them is a fine to medium grained diorite or granodiorite, with less pink potassium feldspar than the Cadillac Mountain Granite.
Works Cited:
Duane & Ruth Bruan. Revised Mount Desert Island Bedrock Geology Map Explination. August 21, 2012
Gilman, A. R., C. A. Chapman, T. V. Lowell., H. W Borns, Jr. (1988). The Geology of Mount Desert Island: A Visitor’s Guide to the Geology of Acadia National Park, 1988. Maine Geological Survey, DEPARTMENT OF CONSERVATION.
Marvinney, R. (2010, October 1). Earth Shattering Events at Mount Desert Island. Retrieved
October 25, 2015. <http://www.maine.gov/dacf/mgs/explore/bedrock/sites/oct10.pdf.>
Wilcock, J., M.-A. Longpré, J. M. De Moor, J. Ross, and M. Zimmerer (2010), Calderas
Bottom-to-Top: An Online Seminar and Field Trip, Eos Trans. AGU, 91(1), 1–2.
Wiebe, R.A.,, D. Smith, M. Sturm, E.M. King, and M.S. Seckler. Enclaves in the Cadillac
Mountain Granite (Coastal Maine): Samples of Hybrid Magma from the Base of the Chamber. J. Petrology (1997) 38 (3): 393-423 doi:10.1093/petroj/38.3.393