June Microphoto of the Month
Clinopyroxene, Mole Hill, Rockingham County. Cross-polarized light (false color).
The large grain in the center of this microphotograph is clinopyroxene (cpx for short), a mineral consisting of calcium, magnesium, iron , silicon and oxygen (Ca(Mg, Fe)Si2O6).
Mole Hill is an ancient volcano. The Mole Hill lavas originated deep beneath the surface, in the Earth’s mantle. The cpx is a piece of the mantle that was carried to the surface during the eruption of the volcano. The spongy rim around the cpx formed when the molten magma reacted with and partially dissolved the cpx crystal. Other minerals visible in this photo are olivine (bright colors) and plagioclase (thin white “splinters”).