CARNOTITE    IN    RIO    BLANCO    COUNTY,  COLO,  111 
The  mineral  carnotite  is  of  use  as  a  source  of  the  rare  elements 
uranium  and  vanadium.  It  is  also  reported  to  have  been  tested  and 
found  to  contain  the  rarer  element  radium."  It  is  readily  dissolved 
in  acids  and  may  be  treated  in  this  way  for  the  commercial  production 
of  uranium  salts.  The  chief  use  of  uranium  is  as  a  pigment  in  painting 
on  porcelain,  in  photography,  and  as  a  color  in  glass  manufacturing.6 
It  has  been  employed  experimentally  in  the  manufacture  of  alloys 
of  iron  and  aluminum.  It  increases  the  hardness  and  elasticit}^  of 
steel  and  also  of  aluminum,  but  as  yet  has  not  been  put  to  much  prac- 
tical use  for  this  purpose. 
A  description  of  the  carnotite  occurrences  in  western  Colorado  and 
a  discussion  of  the  chemical  nature  of  the  mineral  will  be  found  in  a 
paper  published  by  Hillebrand  and  Ransome  in  August,  1900.c  In 
this  paper  the  following  conclusions  as  to  the  general  nature  of  carno- 
tite are  reached: 
The  body  called  carnotite  is  probably  a  mixture  of  minerals  of  which  analysis  fails 
to  re\eal  the  exact  nature.  Instead  of  being  the  pure  uranyl-potassium  vanadate,  it 
is  to  a  large  extent  made  up  of  calcium  and  barium  compounds.  Intimately  mixed 
with  and  entirely  obscured  by  it  is  an  amorphous  substance — a  silicate  or  mixture  of 
silicates — containing  vanadium  in  the  trivalent  state,  probably  replacing  aluminum. 
The  deposits  of  carnotite,  although  distributed  over  a  wide  area  of  country,  arc  for  the 
most  part,  if  not  altogether,  very  superficial  in  character  and  of  recent  origin. 
The  Rio  Blanco  County  carnotite  is  found  in  the  Dakota  sandstone, 
a  group  of  sandstone  ledges  of  which  several  are  very  massive,  inter- 
stratified  with  some  shaly  beds.  This  formation  has  a  thickness  of 
700  feet  or  more.  The  carnotite  is  found  at  the  summit  of  the  hog- 
back ridge  formed  by  the  lowest  and  most  massive  of  the  sandstones. 
In  the  principal  group  of  deposits  seen  the  carnotite  occurs  in  asso- 
ciation with  fossil  or  silicified  wood.  This  fossil- wood  layer  is  appar- 
ently an  original  stratum  of  the  Dakota  sandstone,  for  it  may  be 
traced  along  the  strike  of  the  beds  for  a  mile  or  more.  The  carnotite 
itself  is  in  the  form  of  a  bright-yellow  film  or  crust  with  the  appearance 
of  having  been  deposited  from  solution,  coating  the  silicified  wood 
and  filling  cracks  in  it  and  to  a  less  extent  in  the  neighboring  sand- 
stone. In  only  one  place  the  mineral  was  found  as  an  impregnation 
in  the  Dakota  sandstone  apparently  without  association  of  silicified 
wood. 
The  mineral  itself,  scraped  from  the  rock  to  a  glass  slide,  immersed 
in  liquid  and  covered  with  a  thin  glass,  shows  on  magnification 
minute  granular  patches,  transparent  and  yellow  in  color.  W.  T. 
Schaller  examined  some  of  this  material  in  the  Geological  Survey 
laboratory  and  found  a  few  crystals  showing  minute  hexagonal  form 
q  Pmg.  and  Min.  Jour.,  vol.  77,  1904,  p.  Cull 
&Eng.  and  Min.  Jour.,  vol.  76,  1903,  p.  4(i. 
c  On  carnotite  and  associated  vanadiferous  minerals  in  western  Colorado:  Am.  Jour.  Sci.,  4th  ser. 
vol.  10,  1900,  p.  120. 
Bull.  315—07 8 
