  We report the discovery of a small separation quasar pair (z=0.586, O=18.4,
19.2, sep. = 2.3 arcsec) associated with the radio source FIRST
J164311.3+315618 (S_1400 = 120 mJy). The spectrum of the brighter quasar (A)
has a much stronger narrow emission-line spectrum than the other (B), and also
stronger Balmer lines relative to the continuum. The continuum ratio of the
spectra is flat in the blue at about 2.1, but falls to 1.5 at longer
wavelengths. A K' image shows two unresolved sources with a flux ratio of 1.3.
The different colors appear to result from the contribution of the host galaxy
of B, which is evident from Ca II and high-order Balmer absorption lines
indicative of a substantial young stellar population. New 3.6 cm VLA
observations show that the compact radio source is coincident with quasar A (B
is only marginally detected). We rule out the lensing hypothesis because the
optical flux ratio is A/B = 1.2 to 2, while the radio flux ratio is A/B > 40,
and conclude that this system is a binary. Moreover, the radio-loud quasar is a
compact steep spectrum source. FIRST J164311.3+315618A, B is the lowest
redshift and smallest separation binary quasar yet identified.
