ART. 28 MINERALOGY OF TRIASSIC LIMESTONE SHANNON H 



with dilute acid to remove a little calcite present as impurity. The 

 resulting material was homogeneous garnet but varied in color under 

 the microscope from transparent colorless to brown, the brownest 

 material being faintly anisotropic but grading into the isotropic 

 material with lessening of the color. The analysis gave the fol- 

 lowing results: 



Analysis of slickensided garnet coating 



SiOs 33. 23 



AI2O3 4. 65 



FesOa 26. 37 



FeO . 04 



CaO 34. 18 



MgO Trace 



H2O I 1.79 



Total 100. 26 



The analysis shows the material to be garnet, principally of the 

 lime-iron molecule andradite with a little of the lime-alumina mole- 

 cule, grossularite. 



SERPENTINE 



Serpentine is common though not abundant in the lime silicate 

 rocks as fine scaly interstitial material. It frequently replaces lime- 

 stone pebbles to a slight extent as disseminated grains scattered 

 throughout the pebble. Sometimes small fia6 thin fragments of 

 limestone in the breccia are completely replaced by oil green trans- 

 lucent serpentine when it becomes conspicuous to the naked eye. In 

 other cases a layer of pale yellow green waxy serpentine from a mil- 

 limeter to a centimeter thick surrounds a rounded pebble of dense 

 white marble as a continuous envelope, and penetrates it along 

 cracks. In thin section this serpentine is clearly seen to be a re- 

 placement of the calcite of the marble and to vary from isotropic 

 through fine scaly material of low birefringence to coarser flakes of 

 high birefringence. 



XONOTLITB 



The calcium silicate described as a new mineral from California'' 

 and later shown to be identical with xonotlite® was identified in a 

 single specimen found loose on the floor of the Leesburg quarry by 

 Doctor Schaller. The xonotlite forms rounded patches up to 5 or 6 

 centimeters in diameter, surrounded by rims from 1 to 4 millimeters 

 wide of cross fibered pale bluish green material which is largely 



^ Esper S. Larsen. Eakleite, a new mineral from California. Amer. Journ. Sci., vol. 43, 

 pp. 464-465, 1917. 



* Esper S. Lar.sen. The identity of eakleite and xonotlite. Amor. Mineralogist, vol. 8, 

 pp. 181-182, 1923. 



