^ienth.J 'J*^^ LAusustl.s, 



Groth, Sandberger, and otliers, have established beyond doubt that this 

 change from tlie one mineral into the other is almost universal. 



At that time I have also shown that at Webster, Jackson county, N. 

 C, a foliated talc has in a similar manner resulted from the alteration of 

 chrysolite. The latter alteration has since been observed in most of the 

 localities in the Southern States, where corundum deposits are found asso- 

 ciated with chrysolite rocks. 



In Pennsylvania, where the unaltered chrysolite rock has never been ob- 

 served, a rock has been found which is its representative and contains the 

 same constituents, only in different proportions. In North Carolina the 

 granular chrysolite always contains small quantities of enstatite (bronzite), 

 in Pennsylvania on the contrary we have an enstatite (bronzite) rock, con- 

 taining small grains (from'5 to 10 fo) of chrysolite. It is best developed 

 at Castle Rock, Delaware county, also near Wood's Chrome Mine in 

 Lancaster county. 



In all the chrysolite rocks small grains or crystals of chromite are dis- 

 seminated through the mass of the rock ; in the serpentine, which has re- 

 sulted from the alteration of the chrysolite, these crystals or grgjns are 

 still present and give evidence of the original mineral. This is also the 

 case with a peculiar variety of talc, the so-called "indurated talc," which 

 occurs a few hundred yards south-south-west from'Castle Rock, Delaware 

 county, Pa. It is compact, with a strong lens shows a cryptocrystalline, 

 slightly scaly structure, and an impure grayish-olive green color. H = 2. 

 Sp. G-r. = 2.789. Fracture splintery to subconchoidal ; dull. 



Calculated : 

 61.92 



5.57 



27.86 



4.65 



100.92 100.00 



This is a talc, in which about one tenth of the magnesia is replaced by 

 ferrous oxide = Hj (Mg/|jFeJy);j Sij Oj.,, represented bj" the calculated 

 analysis above given. 



Talc is generally one of the final i^roducts of the alteration of other 

 rocks and minerals, but in this case, it has suffered a veiy remarkable 

 change into anthophyllite. It is enveloped by an aureole of a white 

 or grayish-white mineral, radiating from the nucleus of talc, having a thick- 

 ness of from a few to over 15'"'". The mineral is fibrous, of silky lustre 



