Site 7. Tishomingo Granite.
Tishomingo Granite is exposed at 10 Acre Rock near Troy, Oklahoma.

Figure 32. Exposure of Tishomingo Granite.

Like all intrusive igneous rocks, the granite has large interlocking mineral crystals. The major mineral components are orthoclase feldspar, quartz and minor mafic minerals.

Figure 33. Close up of Tishomingo Granite (nickel for scale). 

The granite exhibits exfoliation jointing (the release of overburden pressure when the rock is exhumed causes it to expand outward and crack into parallel sheets).

Figure 34. Exfoliation jointing in the granite.

On flat surfaces, water collects in depressions forming solution hollows. The water accelerates chemical weathering of the granite, deepening the hollows.

Figure 35. Small solution hollows.

The solution hollows grow larger over time and the decayed granite forms a rudimentary soil.

Figure 36. Soil forming in a large solution hollow (small boy for scale).

Eventually, the soil becomes capable of supporting vegetation.

Figure 37. Vegetation established in a large solution hollow.

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