Generate the augite crystal first, although the order actually doesn't matter in this case. Crystal class is 2/M, monoclinic, and the axes are A=9.8, B=9.0, C=5.25, BETA=105. Forms are:
Go to the Epitaxial Crystals dialog in the Input1 menu and enter the data for hornblende: the crystal class is also 2/M, axes are A=9.9, B=18.0, C=5.3 and BETA=105.5. Forms are:
Specify (100) and [001] as the face and vector of the host, and (-100) and [001] as the face and vector of the guest hornblende. Specify the type as Interpenetration, and center-center Distance of zero. Intercrystal edges should be checked, and you will need to Remove Hidden Lines (Display menu).