March Microphoto of the Month
Microphotos are what they sound like – photographs taken under a microscope. This monthly blog feature will showcase photographs taken of rocks and minerals under the microscope. To prepare a rock for photography, a rock chip is glued to a microscope slide, cut and ground to a thickness of 30 microns – thinner than a human hair - and then polished to a mirror finish. Photos can be taken using light from above that is reflected back to the viewer (reflected light) or light that passes through the specimen from below – transmitted light. Various other techniques can also be applied, and I will discuss them as they appear in this blog. This month’s photo is taken using the reflected light technique.
This is a reflected light photograph (magnification 100x) of a rock collected over a mile beneath the seafloor at the Mid-Atlantic Ridge. The medium-gray material is olivine, an iron-magnesium silicate mineral. When the olivine came in contact with seawater circulating beneath the ridge, it reacted to form the minerals serpentine (darker gray) and magnetite (bright streaks). The cracks in the olivine formed as a result of the volume expansion associated with this reaction.