TIN. 
THE  OCCURRENCE  AND  DISTRIBUTION  OF  TIN. 
By  Frank  L.  IIess  and  L.  C    (Jraton. 
ORES  OF  TIN. 
The  principal  ore  of  tin  is  the  dioxide  (Sn02),  cassiterite.     When 
re  this  mineral  contains  78.G  per  cent  of  metallic  tin,  but  usually 
percentage  is  less,  by  reason  of  the  presence  of  impurities.     In 
Lor  it  is  usually  brown,  but  it  varies  from  white  to  black.     The 
■eak  or  color  of  the  powder  is  white,  grayish,  or  brownish.     Cas- 
erite   crystallizes   in   the   tetragonal   system   and   very   frequently 
|rs  in  well-developed  crystals,  which  are  usually  double  pyramids. 
e  hardness  of  the  mineral  is  between  6  and  7,  or  nearly  that  of 
irtz.     It  has  only  imperfect  cleavage,  but  is  very  brittle,  and  in 
sequence  can  be  easily  crushed.     It  is  practically  insoluble,  and 
ery  resistant  to  weathering  agencies.     One  of  the  characteristics 
assiterite  is  its  high  specific  gravity,  it  being  about  seven  times  as 
vy  as  water  (6.8  to  7.1).     On  account  of  this  high  specific  gravity, 
ins  of  the  mineral  are  transported  by  running  water  with  consid- 
fble  difficulty,  and  are  deposited  at  the  first  opportunity,  forming 
plber  deposits  of  the  so-called  stream  tin.     Over  80  per  cent  of  the 
Jpent  supply  of  tin  comes  from  these  placers. 
■food  tin  is  cassiterite  which  has  been  formed  in  such  a  way  as  to 
pOfess  a  fibrous  structure,  suggesting  the  grain  of  wood. 
ftannite,  or  tin  p}7rites,  a  complex  sulphide  of  copper,  iron,  and  tin, 
0Q||rs  but  rarely  as  an  ore. 
PRODUCTION  AND  CONSUMPTION  OF  TIN. 
lf>r  many  years  the  increasing  world's  production  of  tin  has  been 
uuile  to  keep  pace  with  the  demand,  and  the  consequently  increased 
Jijfc  of  this  metal  has  served  to  stimulate  prospecting  and  mining. 
VoiHthstanding  this,  the  production   for   1904  was   103,134   tons:' 
a  The  short  ton  of  2,000  pounds  is  used  throughout  this  article. 
I Bull.  280—05  m 11  161 
