The absorption spectrum of copper in the synthetic silicate BaCuSi4O10 has been measured in the region 4000–22,000 Å. The spectrum can be interpreted by supposing that the order of increasing energy of the 3d orbitals of the copper is dz2 < dxz,yz < dxy < dx2–y2. The interpretation is supported by quantitative comparison of the spectra of BaCuSi4O10 and BaFeSi4O10(gillespite). A general picture of the electronic structure of the transition-metal ion in the gillespite structure is presented. The 5A1g→5Eg transition in BaFeSi4O10 is briefly discussed.