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Las Choyas, Mun. de Ahumada, Chihuahua, Mexico

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Diggings in a 2 square mile tuffaceous ash flow that produce the "Mexican Coconut" geodes

Ref:
Cross, B. & Culp Zeitner J. (2006): Geodes Natures Treasures, P.11-41

Finkelman, R.B., H.T. Evans, and J.J. Matzko, (1974): Manganese minerals in geodes from Chihuahua, Mexico. Mineralogical Magazine, MARCH 1974, VOL. 39, PP. 549-58.

Hoffmann-Rothe, R. (2006): "Coconuts": Die Knack-Geoden von Las Choyas, Mexiko. LAPIS 31 (11), 47-50

Robert B. Finkelman, John J. Matzko, Ching Chang Woo, John Sampson White & Walter R. Brown (1972): A Scanning Electron Microscopy Study of Minerals in Geodes from Chihuahua, Mexico. Mineralogical Record 3:205-212.




Group 4 - Oxides and Hydroxides
  		• Birnessite4.FL.45
    (Na,Ca)
     
    0.5
    		(Mn
    4+
     
    		,Mn
    3+
     
    		)
     
    2
    		O
     
    4
    		 · 1.5H
     
    2
    		O
  		• Cryptomelane4.DK.10
    K(Mn
    4+
     
    		,Mn
    2+
     
    		)
     
    8
    		O
     
    16
  		• Goethite4.FD.10
    α-Fe
    3+
     
    		O(OH)
  		• Hematite4.CB.05
    Fe
     
    2
    		O
     
    3
  		• Hollandite4.DK.05
    Ba(Mn
    4+
     
    		,Mn
    2+
     
    		)
     
    8
    		O
     
    16
  		• Opal4.DA.10
    SiO
     
    2
    		·nH
     
    2
    		O
  		• Pyrolusite4.DB.05
    MnO
     
    2
  		• Quartz4.DA.05
    SiO
     
    2
  		• Ramsdellite4.DB.15a
    Mn
    4+
     
    		O
     
    2
  		• Ranciéite4.FL.40
    (Ca,Mn)Mn
     
    4
    		O
     
    9
    		·3H
     
    2
    		O
  		• Todorokite4.DK.10
    (Ca,K,Na,Mg,Ba,Mn)(Mn,Mg,Al)
     
    6
    		O
     
    12
    		·3H
     
    2
    		O
    Group 5 - Nitrates and Carbonates
  		• Calcite5.AB.05
    CaCO
     
    3
  		• Siderite5.AB.05
    FeCO
     
    3
    Group 7 - Sulphates, Chromates, Molybdates and Tungstates
  		• Gypsum7.CD.40
    Ca[SO
     
    4
    		] · 2H
     
    2
    		O
    Group 8 - Phosphates, Arsenates and Vanadates
  		• Apatite-(CaOH)
    var: Carbonate-rich Apatite-(CaOH)    		8.BN.05
    Ca
     
    5
    		[(OH,O)|(PO
     
    4
    		,CO
     
    3
    		)
     
    3
    		]
    Group 9 - Silicates
  		• Beidellite9.EC.40
    (Na,Ca
     
    0.5
    		)
     
    0.3
    		Al
     
    2
    		(Si,Al)
     
    4
    		O
     
    10
    		(OH)
     
    2
    		·nH
     
    2
    		O
  		• Kaolinite9.ED.05
    Al
     
    2
    		Si
     
    2
    		O
     
    5
    		(OH)
     
    4
  		• Mordenite9.GD.35
    (Na
     
    2
    		,Ca,K
     
    2
    		)Al
     
    2
    		Si
     
    10
    		O
     
    24
    		·7H
     
    2
    		O
    Unclassified Minerals
  		• 'Chalcedony'-


    19 entries listed. 18 valid minerals.

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