One advantage of a digital camera is the convenient LCD viewfinder that facilitates rotating the specimen while simultaneously previewing the image. Though it is possible to handhold the camera, it is definitely not advisable. Camera motion is the single biggest contributor to blurry images. Set the camera on a sturdy tripod and compose the image by adjusting the tripod. It is best to fill the image as completely as possible with the mineral specimen.
Digital cameras have an LCD screen as the viewfinder.
This provides the exact view the camera is seeing similar to conventional SLR camera. Adjust the lights and add reflectors for reflections and shadows - Reflections off crystal faces and shadows cannot be added later during image editing. Arrange the lights to describe the form, and crystal luster of the specimen. This usually involves primary and secondary reflections, but is a matter of personal taste to the photographer. See Jeff Scovil's book for further discussion on how illuminate a specimen for photography.