AGATES, THE INSIDE STORY: AN UNDERGRADUATE RESEARCH PROJECT AT DELAWARE COUNTY COMMUNITY COLLEGE

As part of the Physical Geology course at Delaware County Community College, students have the option of participating in an honors project. This allows for a deeper understanding of geology by formulating hypotheses and using techniques to analyze the data collected. This semester, along with collecting and analyzing sediments, we cut open agates to examine what was inside. The samples we observed came from various regions in Brazil.

Agate, a common semi-precious silica mineral, is a variety of chalcedony that occurs in bands of varying color and transparency. Agate is essentially quartz (SiO₂), and its physical properties are in general those of that mineral. Agate usually forms in rounded nodules or knobs which need to be sliced open to bring out the internal pattern hidden in the stone.

The formation of Agate is most often from deposition of layers of silica filling voids in volcanic vesicles or other cavities. The layers form in stages with some new layers providing an alternating color. Since the cavities are irregular and uniquely shaped, each Agate forms its own pattern based on the original cavity shape. When a cavity is completely filled, it forms a solid mass of Agate, but often it is only partially filled, leaving a hollow void which often has crystalline Quartz growths on its innermost layer. In some cases, groundwater can become trapped inside the void, causing precipitation of minerals from the fluids.

The results of opening the agates, aside from quartz, deposits of manganese had formed within the agates. This shows that there was manganese in the fluids that got trapped within the agates. The manganese appeared in many different forms such as blades, irradiation, and tightly bound fibers.