DIATOMACEOUS    DEPOSITS    IN    CALIFORNIA. 
445 
SAN    LUIS    QUADRANGLE. 
Diatomaceous  deposits  occur  in  the  Monterey,  Pismo,  and  Santa 
Margarita  formations  (the  last  two  the  equivalent  of  the  lower  Fer- 
nando in  the  Lompoc  quadrangle)  in  the  San  Luis  quadrangle,0 
immediately  north  of  the  Guadalupe  quadrangle.  The  principal 
localities,  according  to  Fairbanks,  are  on  the  mountains  back  of 
Pismo,  in  the  region  of  Arroyo  Grande,  and  along  the  hills  bordering 
the  south  side  of  the  San  Luis  Valley.  Another  bed  of  considerable 
thickness  occurs  on  the  slope  of  the  San  Luis  Range  south  of  Morro 
Bay,  and  similar  deposits  appear  at  various  points  along  Salinas  Val- 
ley, extending  as  far  up  as  Rinconada  Valley.  These  diatomaceous 
deposits  are  white  and  of  chalky  texture,  as  at  the  typical  localities 
in  the  Lompoc  quadrangle. 
PHYSICAL    AND    CHEMICAL    PROPERTIES 
Diatomaceous  earth  when  pure  is  white  or  gray  in  color,  light  in 
weight,  and  easily  pulverized  to  a  fine  powder.  Owing  to  the  angular 
nature  and  hardness  of  its  component  particles  it  has  valuable  abra- 
sive properties.  It  also  has  great  absorptive  powers,  but  is  very 
resistant  to  weathering.  Chemically  it  is  composed  essentially  of 
opaline  or  colloidal  silica  and  water,  in  general  associated  with  minor 
quantities  of  alumina,  iron  oxide,  lime,  and  magnesia  as  impurities. 
Diatomaceous  earth  is  not  soluble  in  acids  under  ordinary  conditions, 
but  is  easily  dissolved  in  the  stronger  alkalies.  As  chalk,  with  which 
diatomaceous  earth  is  sometimes  confused,  is  soluble  in  acid,  the  two 
may  be  distinguished  by  the  acid  test. 
The  following  table  gives  3  analyses  of  samples  of  the  shale  (slightly 
hardened  diatomaceous  earth)  from  the  Lompoc  quadrangle,  together 
with  analyses  of  similar  diatomaceous  material  from  other  localities: 
Analyses  of  diatomaceous  earths  or  shales. 
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
9. 
Silica  (Si02)  
65.62 
86.92 
4  27 
72.50 
11.71 
2.35 
.32 
.83 
1.88 
9.54 
86.89 
2.32 
1.28 
0.43 
Trace. 
3.58 
4  89 
86.90 
4  09 
1.26 
.14 
.51 
1.18 
5.99 
80.53 
5.89 
1.03 
.35 
80.66 
3.84 
'".'08' 
81.53 
3.43 
3.34 
2.61 
84  15 
Alumina  (AI2O3) 
1.40 
Iron  oxide  (Fe203) 
.70 
Lime  (CaO).. 
1.  60 
Trace. 
2.48 
5. 13 
1.  75 
1.10 
Alkalies  ( K2O  +  Na^O) 
2.59 
6.04 
Water  (H20) 
ii.66 
12.03 
14  04 
10.40 
100.  40 
99.  13 
99.39 
100.  07 
99.  83 
99.12 
99.54 
99.50 
1.  Soft  shale,  Harris,  Santa  Barbara  County,  Cal.    Analyst,  W.  T.  Schaller,  1907. 
2.  Porcelain  diatomaceous  shale,  Point  Sal,  Santa  Barbara  County,  Cal.    Fairbanks,  H.  W.,  Bull. 
Dept.  Geol.,  Univ.  California,  vol.  2,  1896,  p.  12.     Specific  gravity  2.12. 
3.  Soft  shale,  Orcutt,  Santa  Barbara  County,  Cal.     Analyst,  W.  T.  Schaller,  1907. 
4.  Monterey,  Monterey  County,  Cal.     Lawson,  A.  C,  and  Posada,  J.  de  la  C,  Bull.  Dept.  Geol.,  Univ. 
California,  vol.  1,  p.  25.    Specific  gravity  1.8-2.1. 
5.  Fossil  Hill,  Nevada.     Bull.  California  State  Min.  Bur.  No.  38,  1906,  p.  28. 
6.  Lake.  Umbagog,  New  Hampshire.    7.  Morris  County,  New  Jersey.    8.  Popes  Creek,  Maryland. 
Merrill,  G.  P.,  Rept.  U.  S.  Nat.  Mus.  for  1899,  p.  220. 
9.  Hanover,  Germany.    Bull.  California  State  Min.  Bur.  No.  38,  1906,  p.  28. 
a  Geologic  Atlas  U.  S.,  San  Luis  folio,  No.  101,  U.  S.  Geol.  Survey,  1904,  p.  14  and  economic  geology 
sheet. 
Bull.  315—0^ 
29 
