﻿508 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  alumina, 
  occurring 
  as 
  six 
  sided 
  plates 
  or 
  irregular 
  scales 
  nsnally 
  

   of 
  a 
  dark 
  color. 
  As 
  it 
  decomposes 
  easily 
  with 
  the 
  formation 
  of 
  

   iron 
  oxid, 
  it 
  is 
  not 
  as 
  commonly 
  found 
  in 
  clays 
  as 
  muscovite. 
  The 
  

   latter 
  is 
  sometimes 
  called 
  potash 
  mica, 
  though 
  it 
  also 
  contains 
  a 
  

   sjnall 
  amount 
  of 
  iron 
  and 
  magnesia. 
  It 
  is 
  of 
  a 
  silvery 
  white 
  or 
  

   light 
  brown 
  color. 
  

  

  As 
  before 
  mentioned, 
  mica 
  by 
  itself 
  is 
  rather 
  refractory, 
  but 
  in 
  

   the 
  presence 
  of 
  other 
  minerals 
  may 
  serve 
  as 
  a 
  flux 
  at 
  high 
  tem- 
  

   perature. 
  Even 
  in 
  burned 
  bricks 
  the 
  mica 
  scales 
  are 
  often 
  per- 
  

   ceptible. 
  This 
  is 
  frequently 
  the 
  case 
  when 
  the 
  brick 
  has 
  been 
  

   burned 
  at 
  a 
  temperature 
  of 
  2500° 
  F. 
  

  

  Siderite. 
  This 
  is 
  perhaps 
  a 
  more 
  common 
  constituent 
  than 
  is 
  

   usually 
  imagined. 
  It 
  generally 
  occurs 
  in 
  the 
  form 
  of 
  opaque, 
  

   rounded 
  masses, 
  and 
  effervesces 
  on 
  the 
  addition 
  of 
  warm 
  muriatic 
  

   acid. 
  In 
  the 
  burning 
  of 
  the 
  clay 
  siderite 
  or 
  iron 
  carbonate 
  is 
  

   converted 
  into 
  iron 
  oxid. 
  

  

  Pyrite. 
  This 
  is 
  a 
  combination 
  of 
  iron 
  and 
  sulfur. 
  It 
  has 
  a 
  

   metallic 
  luster 
  and 
  yellow 
  color, 
  and 
  is 
  a 
  very 
  common 
  constituent 
  

   of 
  many 
  fire 
  clays, 
  occurring 
  either 
  in 
  the 
  form 
  of 
  small 
  yellow 
  

   metallic 
  grains 
  or 
  concretionary 
  masses 
  of 
  yellow 
  crystals. 
  In 
  the 
  

   burning 
  of 
  clay 
  it 
  may 
  be 
  changed 
  to 
  sulfate 
  of 
  iron 
  and 
  if 
  the 
  

   clay 
  is 
  heated 
  to 
  vitrification, 
  it 
  will 
  serve 
  as 
  a 
  flux. 
  The 
  brick 
  

   makers' 
  common 
  name 
  for 
  pyrite 
  nodules 
  is 
  " 
  sulfur-balls 
  ''. 
  

  

  Marl 
  or 
  limestone 
  fragments. 
  The 
  action 
  of 
  these 
  is 
  the 
  same 
  

   as 
  that 
  of 
  calcite. 
  Their 
  presence 
  may 
  be 
  detected 
  by 
  treatment 
  

   with 
  muriatic 
  acid. 
  

  

  Dolomite, 
  the 
  double 
  carbonate 
  of 
  lime 
  and 
  magnesia, 
  and 
  mag- 
  

   nesite, 
  the 
  carbonate 
  of 
  magnesia, 
  may 
  both 
  occur 
  in 
  clay, 
  either 
  

   as 
  earthy 
  grains 
  or 
  as 
  rhombohedral 
  crystals. 
  Either 
  alone 
  is 
  highly 
  

   refractory 
  and 
  in 
  this 
  condition 
  is 
  used 
  as 
  linings 
  for 
  furnaces, 
  but 
  

   when 
  present 
  in 
  clay 
  may 
  serve 
  as 
  a 
  flux, 
  their 
  action 
  being 
  similar 
  

   to 
  that 
  of 
  lime. 
  

  

  Iron 
  oxid. 
  This 
  is 
  perhaps 
  the 
  most 
  common 
  impurity 
  of 
  clay 
  

   next 
  to 
  quartz. 
  It 
  may 
  occur 
  in 
  the 
  form 
  of 
  eai'thy 
  grains, 
  or 
  

  

  