Large single crystals of the garnet imanite, Ca3Ti2Si3O12, were synthesized by a floating zone technique. Near-infrared to visible spectroscopy presents an optical gap of 1.65 eV at 4 K, proving the insulating character of this garnet compound. Electron paramagnetic resonance data indicate that the d(1) electron of Ti3+ exhibits an orbital contribution to the spin moment (g = 1.859(1)). An antiferromagnetic state is observed below T-N = 7 K, confirmed by magnetic susceptibility and specific heat data. X-ray diffraction investigations on powders and single crystals of imanite reveal that the crystal structure agrees well with expectations: the cubic symmetry Ia3 (d) over bar describes all obtained single crystal and powder diffraction data.