Gemini is a four-circle diffractometer with kappa geometry for structure analysis of single crystals. It has two x-ray sources: Mo sealed x-ray tube with grapphite collimator and Mo-Enfance collimator, and Cu sealed x-ray tube with mirror optics. Diffracted beams are detected by 135mm diameter 2k x 2k CCD detector Atlas with dynamic range 18 bits. The size of the investigated samples should ideally be between 0.1 and 0.5 mm. The samples can be anything from metals to large organic molecules, except proteins which require different technology.