GRAPHITE consists of hexagonal crystals. Thus the optical constants depend on the direction of the incident light. For light with an electric vector parallel to the basal planes of the crystals graphite behaves like a metal. In the perpendicular direction, for light propagation through a crystal with an electric vector along optic axis, it behaves like a dielectric particle. Many calculations on graphite as interstellar matter have been made. In these cases the electric vector is in the basal plane. Lenham and Treherne have measured the optical constants for graphite with the electric vector along the optic axis (Figs. 1 and 2)1. These figures show a sharp minimum in the optical conductivity 2 nk/λ at a wavelength λ = 0.64µ and a maximum at the same wavelength in the real part of the dielectric constant n2–k2. In the computer programme of Q extinction for spherical particles, “n” and “k” have to be used. They are calculated from 2 nk/λ and n2–k2 at different wavelengths. The optical constants “n” and “k” have sharp maximum respectively minimum at λ = 0.64&µ which produces the typical appearance of the Q extinction curves (Fig. 3). The diagram shows a broad and deep depression around λ = 0.64µ between the wave-numbers l.5µ−1 and 2.0 µ−1 for different particle radii. No other material with a similar appearance has been reported which could be interstellar grains. Pure ice is also a dielectric material, but both “n” and “k” are independent of wavelength and give no depression in the Q curves.