Abstract
Modal analysis of stained granite slabs is performed using image processing software “Adobe photoshop TM”with personal computer and scanner. The areas corresponding to the rock-forming minerals of [K-feldspar], [plagioclase], [quartz+mafic minerals] and [mafic minerals] are selected from a digital image of the slabs. The procedure was carried out on the basis of RGB color similarity. K-feldspar, plagioclase and mafic minerals were recognized independently, however, it is difficult to distinct quartz and mafic minerals due to color similarity. Human support is required to obtain more acurate modal data.
The accuracy of modal data by this method depends on a quality of input image and sample size. 400 dpi digital image is suitable. Slab sizes of medium-grained and coarse-grained granite are more than 9 and 12 cm2 respectively. The values measured by the employed method are consistent with those estimated by so called point-counting method. Modal analysis by the method is very useful except for fine-grained and muscovite-bearing granite.
