A naturally occurring, iron rich silicate mineral commonly known as biotite has been found to perform very well as a Brewster angle reflection polarizer in the region 1100 Å to nearly 6000 Å. This observed behavior is somewhat anomalous since it is well‐known that nonabsorbing dielectric surfaces which polarize well in Brewster angle reflection have low reflectivity whereas the light reflected from highly reflecting surfaces has a low polarization. In contrast to this, we have found biotite to have a rather high reflectivity with strong polarization of the reflected light. The characteristics of this polarizer are reported in this paper and the apparent anomaly is resolved in terms of an optical anisotropy hitherto disregarded in this context.