Sterling Pond lies to the northeast of Spruce Peak in a shallow depression along the divide of the mountain. This location is anomalous for a pond because the amount of higher land around it is so small that only a limited amount of drainage area is available for the accumulation of rain and snow. Yet, the outflow of water is almost continuous during the summer. The basin occupied by the pond was probably scoured out by the glacier.
The Sterling Pond area contains talc deposits which probably would be commercial if they were not so inaccessible for mining. These deposits have been studied by A. H. Chidester of the United States Geological Survey and a report is obtainable from the U. S. Government. The occurrence of the talc, as mapped by Chidester, is shown in the sketch of [Figure 8].
Talc has the composition of Mg₃Si₄O₁₀(OH)₂ and is a soft flaky white mineral. The talc-bearing rocks in this area are white, light gray, or light green and usually are irregularly stained yellow-brown by the weathering of an iron-bearing mineral that occurs with the talc. Because of its extremely soft nature, the talc does not form prominent rock exposures. As shown by the figure, the talc can be most easily observed along the shore of Sterling Pond, south of the Green Mountain Club cabin, or along the trail to Smugglers Notch near the top of the first rise from the pond. Here the talc is exposed in the trail as low, rounded, slippery knobs of “messy looking” yellow-brown rock.
As part of the pond is underlain by talc, it is probable that the softness of the talc was a factor in the differential erosion of the basin by the continental glacier.
The talc is believed to have originated by the alteration of a body of ultramafic igneous rock, which is characterized by having a low silica content and a high magnesium content. Sometime during the mountain-building period, the ultramafic igneous rock invaded the pre-existing rocks from an unknown source within the earth’s crust. It is believed that at a later date the original minerals in the igneous rock were altered to talc and other minerals by the action of hot ascending solutions composed principally of water.
Figure 8. Sketchmap showing the location of the talc-bearing rocks at Sterling Pond.
MAP OF THE STERLING POND AREA FOREST BOUNDARY Green Mountain Club cabin STERLING POND To Smugglers Notch EXPLANATION Talc-bearing rock Solid areas are positions of exposures Postulated boundary of talc body beneath pond Trail To Spruce Peak From report by A. H. Chidester
The Long Trail passes by Sterling Pond, where the Green Mountain Club has erected a small cabin overlooking the pond. [Figure 9] is the picturesque view of Mount Mansfield taken from the cabin.