Nah, your relative K ranges are a bit off -
A sandstone is typically in the range of 10^-4 to 10^-8 cm/sec, while an unfractured igneous rock is in the range to 10^-8 to 10^-12. However, for a fractured igneous rock is considerably more permeable (10^-2 to 10^-6 cm/sec), obviously due to preferential flow through the cracks and voids (Freeze & Cherry, 1979). A lot of your permeability assumptions will bepend on your definintion of thyour Representative Elementary Volume that you are using, e.g. a small volume, like Columbia Boulder or Big Joe, could be assumed somewhat homogenous and unfractured. However, if your REV is somewhat larger (Mt. Stuart, Supercrack Buttress), then you have to tak into account both mineralogical heterogenity and areal fracturing, which will increase your hydraulic conductivity values accordingly.