The absolute cosmogenic production of 21Ne (21Nec) and 3He (3Hec) in olivine (Fo81) is measured for the well-dated Tabernacle Hill flow. Values scaled to sea level and high latitude (>60¿) are 45 atoms/g/yr for 21Nec and 109 atoms/g/yr for 3Hec for the past 17,800 years. Production rates for 21Nec are about 50% higher than the theoretical values given by Lal [1991>. A ratio of 21Nec/3Hec of 0.41¿0.05 is measured in olivines that have a range of 25 in cosmogenic exposure; there is no evidence of 3Hec loss in samples older than 100,000 years. Volcanic plagioclase is shown to be a suitable mineral for cosmogenic 21Nec dating of surfaces. 21Nec in co-existing plagioclase and olivine phenocrysts have a constant ratio of 0.42¿.04 in samples with more than 106 atoms of 21Nec. Using all of the 21Nec data and the 3Hec as a cosmic ray flux monitor, production of 21Nec in Ab36 plagioclase is calculated at 16.8¿1.7 atoms/g-yr for the past 17,800 years. The production of 21Nec from 23Na is estimated at 160¿50 atoms/g/yr at 60¿ and sea level or equivalent to that on 24Mg. ¿ American Geophysical Union 1992