American Mineralogist Garnet Images

These color images accompany Lang, H.M. (1996) Pressure-temperature-reaction history of metapelitic rocks from the Maryland Piedmont on the basis of correlated garnet zoning and plagioclase-inclusion composition. American Mineralogist, 81, 1460-1475.





Fe/(Fe + Mg)
Figure 3. Color X-ray maps of mole fractions of grossular, pyrope, spessartine, and almandine components and Fe/(Fe+Mg) in the modeled garnet from sample HV104. Reds represent high concentration of a component, blues and purples represent low concentration. The color scale for grossular, pyrope and spessartine ranges from 2 to 15 mole percent. The color scale for almandine and Fe/(Fe+Mg) ranges from 70 to 91 mole percent. All images representan area 6.5 mm wide by 6.9 mm high. The line of the detailed traverse discussed in the text goes from the bottom center of the garnet to the top center. Note the irregular high-grossular, low-almandine region in the core of the garnet, and the abundant plagioclase inclusions in the intermediate region (bright spots on grossular image).

Figure 5. Molar X-ray maps of anorthite content of plagioclase inclusions and grossular in adjacent garnet. (A) Anorthite content of plagioclase for the whole garnet (at the same scale as the garnet images of Fig. 3). Note the reds in the high-anorthite plagioclase inclusions in the core, the greens and blues of plagioclase inclusions in the inclusion-rich intermediate region, and the lower anorthite plagioclase outside the garnet.(color scale: 23-45 mol% anorthite). The area enlarged in the two images at right includes the four large inclusions that form a diamond-shaped pattern in the lower center of the garnet. (B) A more detailed map of mole fraction anorthite in plagioclase in a portion of the garnet. The center of the garnet is toward the upper right, and the image covers an area 1.3 mm wide and 1.8 mm high. All the plagioclase inclusions are normally zoned with higher anorthite in their cores and lower anorthite in the rims. Both the core and rim of the uppermost plagioclase inclusion are warmer colors, indicating higher anorthite content. (C) A detailed map of mole fraction grossular for the same portion of the garnet as in the previous image. Grossular zoning in the garnet progresses from high values (red) in the upper right corner, which is near the core, to low values (blue) at the bottom of the map, which is near the rim. There is no independent zoning in grossular around individual plagioclase inclusions (bright areas).