LIME  AND  MAGNESIA. 
SOME  MAGNESITE  DEPOSITS  OF  CALIFORNIA. 
By  Frank  L.  Hess. 
INTRODUCTION. 
Magnesite,  while  not  a  common  mineral,  is  found  at  a  considerable  number  of  places  in 
different  parts  of  the  world  where  there  are  large  areas  of  serpentine,  peridotites,  and 
pyroxenites.  The  principal  foreign  deposits  now  worked  are  in  Germany,  Austria,  Greece, 
Italy, a  and  India,  b  Unworked  deposits  are  known  in  Lapland,  Sweden,  Russia,  Africa, 
Quebec,  c  near  Atlin  Lake,  British  Columbia,  and  in  Mexico,  of  which  the  deposits  in  Quebec 
may  be  altered  sedimentary  rocks. 
In  the  United  States  the  most  important  occurrences  are  in  California,  with  lesser  ones  in 
Southern  Oregon,  Nevada,  Pennsylvania,^  Maryland/  and  Massachusetts. 
The  Pennsylvania  and  Maryland  deposits  were  at  one  time  worked  in  a  small  way  and 
the  product  used  for  making  Epsom  salts  and  other  chemicals,  but  magnesite  from  Austria 
and  Greece  can  now  be  imported  so  cheaply  that  they  no  longer  pay  to  operate. 
In  California  there  are  many  deposits  scattered  along  the  Coast  Range  from  the  Oregon 
line  to  below  Los  Angeles,  with  a  few  along  the  foothills  of  the  Sierras.  Deposits  are  worked 
near  Livermore  and  Porterville,  and  mines  were  formerly  operated  at  Chiles  Valley,  Pope 
Valley,  and  in  a  desultory  way  at  other  points.  The  four  places  mentioned  were  visited 
by  the  writer  in  November,  1905. 
COMPOSITION  AND  USES. 
Magnesite,  as  it  occurs  in  the  California  deposits,  is  a  beautiful  white  fine-grained  rock 
with  a  conochoidal  fracture  that  looks  like  a  break  in  fine  china.  It  is  magnesium  carbon- 
ate, MgC03,  and  is  about  one-third  harder  and  heavier  than  calcite.  It  contains  52.4  per 
cent  of  carbon  dioxide  (C02)  and  47.6  per  cent  of  magnesia  (MgO).  Like  limestone,  it 
gives  off  carbon  dioxide  on  burning,  and  it  is  used  for  producing  this  gas,  as  the  proportion 
contained  is  much  greater  than  in  limestone,  which  carries  but  44  per  cent.  The  residual 
magnesia  left  on  burning  is  also  more  valuable  than  the  lime  left  on  burning  limestone,  and 
the  amount  of  heat  required  to  drive  off  the  C02  is  less.  The  burned  magnesia  (MgO)  is 
used  for  making  refractory  brick  for  use  with  basic  slags,  as  in  copper  smelting  and  some 
steel  making,  as  an  adulterant  in  paint,  and  medicinally.  After  being  changed  to  the  sul- 
phite it  is  used  in  the  digestion  of  wood  pulp  for  paper.  The  light  carbonate,  known  also 
as  magnesia  alba  levis,  is  employed  for  medicinal  and  toilet  purposes,  and  with  varying 
a  D'Achiardi,  Giovanni,  La  formazione  della  magnesite  all'  Isola  d'Elba:  Atti  della  Societa  toscana 
di  scienze,  naturale,  residentein  Pisa;  Memorie,  vol.  20,  1904,  pp.  86-134,  3  pis. 
b  Eckel,  Edwin  C,  Cements,  Limes,  and  Plasters,  their  materials,  manufacture,  and  properties,  New 
York,  John  Wiley  &  Sons,  1905,  p.  150. 
c  Hoffman.  G.  C,  Kept,  section  of  chemistry  and  mineralogy:  Ann.  Rept.  Canadian  Geol.  Survey, 
Ottawa,  vol.  13,  1905,  pp.  14-19. 
d  Frazier,  P.,  jr.,  Lancaster  County:  Second  Geol.  Survey  Pennsylvania,  vol.  CCC,  1880,  pp.  89,  97, 
176-179,  196. 
«  Bascom,  F.,  The  geology  of  the  crystalline  rocks  of  Cecil  County:  Cecil  County  report,  Maryland 
Geol.  Survey,  1902,  pp.  96-97. 
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