IDENTITY OF THE SERPENTINE. 113 



Talc occurs abundantly in the nietamorplilc areas of the gold belt, 

 and the Survey collections contain fine specimens from that region. Ac- 

 cording to Mr. IT. G. Hanks it is also found at two or three localities in the 

 Coast Ranges. Nothing would be less surprising' than the discovery in 

 the Coast Ranges of serpentines containing- flakes of talc such as are de- 

 scribed by Hussak, but this combination is not as yet known to occur 

 The analyses also exclude deweylite and the minerals allied to it. It still 

 rempins possible that some hitherto unrecognized mineral closely allied to 

 serpentine enters into the serpentinoid mass, but the gradation of prop- 

 erties is so complete that this seems improbable. The variations in the col- 

 ors of polarization possibly correspond to the replacement of a greater or 

 smaller portion of magnesium by iron, accompanying which there is likely 

 to be a change in the angle of the optical axis. This angle is known to 

 vary greatly in serpentines. The higher color in natural light of the por- 

 tions which polarize most vividly may be due to the presence of ferric 

 oxide as an impurity. The association of a partial replacement of mag- 

 nesium by iron and a separation of a little iron oxide would not be 

 unnatural. 



The mineral described as antigorite by Mr. Eichstiidt corresponds in 

 most respects to that described by Mr. Hussak and otliers and to the ser- 



UL-arly to tUe point at wliicla balsam softens. It -svas soon fonud that the serpentine was attacked. 

 Fresh portions of acid were added from time to time, and at hist it appeared thiit most of the serpen- 

 tine was decomposed, leaving a colloidal mass. Some portions iu immediate contact with the quartz 

 grain at points where indentation had been observed appeared to be entir.ly converted into gelati- 

 nous silica. The portions which were only partially decomposed almost ceased to give interference 

 colors. At the edge of the acid drop upon the cover there formed prisms supposed to be magnesium 

 chloride, giving angles of extinction of over 30°. The solution was washed off, evaporated on asecond 

 <rlass and sulphuric acid added. Prisms giving a low angle of extinction formed on partial evapora- 

 tion. On evaporating until fumes of sulphuric anhydride were given off, the hexagonal scales ap- 

 peared, and on stamling a few moments uuderthe microscope these uniaxial crystals deliquesced. The 

 substance under examination was thus certainly a magnesium silicate, and not a talcose mixture. No 

 other crystals made their ,api>earance. To test the behavior of chlorite a pseudodiahase (No. 2G6, Sulphur 

 Bank) was selected and a portion, exposed throngh a perforated cover, was treated with chlorhydrio acid 

 exactly as the serpentine had been. There was no evidence under the microscope of any attack, even 

 after repeating the treatment several times. On boiling powder from the same specimen iu chlorhydric 

 acid it was found that the chlorite was decomposed when the acid was strong, but not when it was 

 dilute. Both magnesia and alumina went into solution. It is probable therefore, but not certain, 

 that this chlorite is the prochlorite of Dana. TUe highly dichroitic serpentine (from No. 21, New Al- 

 madeu) was similarly tested. It dissolved iu warm, dilute chlorhydric acid in the thin section and 

 when the pulverized rock was boiled iu strong acid magnesia, but no sensible quantity of alumina was 

 dissolved. 



MON XIII 8 



