We here report the observation of precipitation patterns obtained when solid zirconium is allowed to react for few seconds with molten aluminum in the temperature range 720 < T < 850 degrees C. The patterns are made by precipitates of the intermetallic compound Al3Zr in the Al matrix. Generally, these precipitates show interconnected wavelike structures, but in a narrower temperature range (780 < T < 820 degrees C), part of these structures further organize into periodic bands. The pattern formation in the Al-Zr system is characterized by the strictly binary nature of the system, the short time scale for the pattern formation, and the presence, in the same sample, of different degrees of periodic organization.