Notwithstanding the great progress which Mineralogy has made of late years, towards the division of minerals into accurate and well defined species, there are several groups which occur in the oldest mineral systems extant, and which have continued to the present time with very little alteration or improvement. I allude to the minerals classed under the names of Asbestus, Chlorite, and Talc. As these minerals, with the exception of certain varieties of talc, have never been observed in crystals, the important labours of the crystallographer have not been able to throw any light upon them. But, as all mineral species are chemical compounds, and as each species consists of the same constituents united in the same proportions, I thought it not unlikely that an accurate chemical analysis of the different varieties of minerals, at present classed under the names Asbestus, Chlorite, and Talc, would be likely to throw considerable light on their nature, and would inform us whether they constitute peculiar mineral species, or are only varieties of species already well defined and characterized. I propose, in this paper, to give an account of the result of this investigation.