This sample also had recognizable hornblende, evidently not completely isolated by magnetic separation.' 'The 'pyroxene concentrate' (DOME-IP) was dominated by orthopyroxene and much less clinopyroxene.
Because it was composed of finer particles (170-270 mesh), it contained far fewer mafic particles with attached glass fragments than DOME-IH.
9), the K-Ar method cannot be used to date samples that are much younger than 6,000 years old (Dalrymple, 1991, p.
93)Cambridge, Massachusetts, USA, performed the K-Ar dating for Austin et al. However, when they did, their website clearly stated in a footnote that their equipment could not accurately date rocks that are younger than about 2 million years old ("We cannot analyze samples expected to be younger than 2 M.
Clearly, basic crystal chemistry and physics dictates that zoned and other relatively large phenocrysts grew deep within the Earth and existed before the glass matrix that rapidly formed during the 1986 eruption.
Similarly, Swenson also fails to comprehend the indisputable history that is associated with the plagioclase zoning and to properly recognize the important age differences between the coarsest phenocrysts and the volcanic glass.
I've attempted to separate very fined-grained minerals from glass in coal ashes by using magnetic separation and hydrofluoric and other acids. Austin even admits that the dacite is 45% phenocrysts and 'lithic (rock) inclusions.'Although Austin claimed that he took precautions to avoid laboratory contamination and that he and his team removed the obvious xenoliths from the dacite sample, Austin's own words refute Swenson's illusions that the dacite mineral/glass 'fractions' were suitably 'pure' enough for testing the validity of the K-Ar method.
This preparation is the purest mineral concentrate.'However, because Austin ignores the analytical inadequacies of Geochron's mass spectrometer (hypothesis #2), except for possibly the pyroxenes, there is no evidence that excess argon is present in any of the other mineral or glass components in this sample.'Another critic said that Dr Austin should only have dated the volcanic glass from his sample, because the glass would have solidified when the lava dome formed.
However, Dalrymple  found that even volcanic glass can give wrong ages and rationalized that it can be contaminated by argon from older rock material.'Clearly, Swenson simply assumes that the volcanic glass contains 'excess argon.' However, dating a mixture of older plagioclase and younger volcanic glass with inadequate equipment (hypothesis #2) does not prove that any of these components contain excess argon.
Y."; also see discussions by advanced equipment, 'memory effects' can be a problem with very young samples (Dalrymple, 1969, p. That is, very tiny amounts of argon contaminants from previous analyses may remain within the equipment, which precludes accurate dates for very young samples.
For older samples, which contain more 40Ar, the contamination is diluted and has insignificant effects. De Paolo, 1998, 'Intercalibration of Standards, Absolute Ages and Uncertainties in 40Ar/39Ar Dating', Chem.