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Los Archipelago (Los Islands), Guinea

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(Iles de Los)

Los Archipelago is located 5 km offshore of Conakry, located on Kaloum Peninsula. It is a ring structure formed by peralkaline nepheline syenites and later phonolitic dykes and pegmatites.

Two magmatic suites are known : one is miaskitic, the other is agpaitic. The difference between this two kind of petrographic suite is linked to the different mineralogy (augite, hastingsite, zircon, titanite in the miaskitic one; aegirina, arfvedsonite, Zr-Ti-Nb-REE silicates for the agpaitic suite).

Iles de Los are the type locality for villiaumite and serandite, described by Lacroix in 1908 and 1931 respectively.

Odinite was discovered in sea floor sediments at the mouth of the Koukoure (Konkouré) River near the islands.

References:
-Lacroix, A. (1908). Sur l’existence du fluorure de sodium cristallisé comme élément des syénites néphéliniques des îles de Los. C. R. Acad. Sci. Paris, 146, 213-216.
-Lacroix, A. (1911). Les syénites néphéliniques de l’archipel de Los et leurs minéraux. Nouv. Arch. Mus. Hist. Nat., 3, 1-132.
-Lacroix, A. (1924). Nouvelles observations sur les syénites néphéliniques des Iles de Los (Guinée). C. r. hedb. Séanc. Acad. Sci., Paris, 178, 1109-1114.
-Lacroix, A. (1931). Les pegmatites de la syénite sodalitique de l’île Rouma (archipel de Los, Guinée française). Description d’un noveau minéral (sérandite) qu’elles renferment. C. R. Acad. Sci. Paris, 192, 189-194.
-Parodi, G. C., & Della Ventura, G. (1987). Steacyite from the Rouma Isle (Los Islands, Republic of Guinea). Neues Jarbuch fur Mineralogie, Mh., Jg. 1987, H. 5, 233-239
-Moreau, C., Ohnenstetter, D., Demaiffe, D., & Robineau, B. (1996). The Los Archipelago nepheline syenite ring-structure: a magmatic marker of the evolution of the central and equatorial Atlantic. Canadian Mineralogist, 34: 281-299.
-Parodi, G. C., & Chevrier, V. (2004). New discoveries in nephelinites from Los island (Republic of Guinea). 5th International Conference "Mineralogy & Museums", Paris, Sept. 5-8th 2004, Bull. de Liaison de la Soc. Franç. de Minéralogie et Cristallographie, 2004, Vol 16, N°2.
-Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.





Map Reference: 9°30'N , 13°50'W

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Mineral list contains entries from the region specified including sub-localities


Mineral List:
  		•  Aegirine
    NaFe
    3+
     
    		[Si
     
    2
    		O
     
    6
    		]
    Reference: [Moreau, C., Ohnenstetter, D., Demaiffe, D., & Robineau, B. (1996). The Los Archipelago nepheline syenite ring-structure: a magmatic marker of the evolution of the central and equatorial Atlantic. Canadian Mineralogist, 34: 281-299]
    Site Photo
    Los Archipelago (Los Islands), Guinea
    © Cristian B.
  		•  Albite
    Na[AlSi
     
    3
    		O
     
    8
    		]
    Reference: []
  		•  'Albite-Anorthite Series'
    Reference: []
  		•  Analcime
    Na
     
    2
    		[Al
     
    2
    		Si
     
    4
    		O
     
    12
    		] · 2H
     
    2
    		O
    Reference: [Lacroix, A. (1911). Les syénites néphéliniques de l’archipel de Los et leurs minéraux. Nouv. Arch. Mus. Hist. Nat., 3, 1-132. ]
  		•  Andradite
    Ca
     
    3
    		Fe
    3+
    2
    		[SiO
     
    4
    		]
     
    3
    Reference: []
  		•  Andradite
    var: Melanite
    Reference: []
  		•  Apatite-(CaF)
    Ca
     
    5
    		[F|(PO
     
    4
    		)
     
    3
    		]
    Reference: []
  		•  Arfvedsonite
    [Na][Na
     
    2
    		][Fe
    2+
    4
    		Fe
    3+
     
    		][(OH)
     
    2
    		|Si
     
    8
    		O
     
    22
    		]
    Reference: [Moreau, C., Ohnenstetter, D., Demaiffe, D., & Robineau, B. (1996). The Los Archipelago nepheline syenite ring-structure: a magmatic marker of the evolution of the central and equatorial Atlantic. Canadian Mineralogist, 34: 281-299. ]
  		•  Astrophyllite
    (K,Na)
     
    3
    		(Fe,Mn)
     
    7
    		Ti
     
    2
    		Si
     
    8
    		O
     
    24
    		(O,OH)
     
    7
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Augite
    (Ca,Na)(Mg,Fe
    2+
     
    		,Al,Fe
    3+
     
    		,Ti)[(Si,Al)
     
    2
    		O
     
    6
    		]
    Reference: [Moreau, C., Ohnenstetter, D., Demaiffe, D., & Robineau, B. (1996). The Los Archipelago nepheline syenite ring-structure: a magmatic marker of the evolution of the central and equatorial Atlantic. Canadian Mineralogist, 34: 281-299. ]
  		•  Biotite
    Reference: []
  		•  Britholite-(Ce)
    Ca
     
    2
    		(Ce,Ca)
     
    3
    		[(OH,F)|(SiO
     
    4
    		,PO
     
    4
    		)
     
    3
    		]
    Reference: [G.C. Parodi and V. Chevrier : "New discoveries in nephelinites from Los island (Republic of Guinea)", 5th International Conference "Mineralogy & Museums", Paris, Sept. 5-8th 2004, Bull. de Liaison de la Soc. Franç. de Minéralogie et Cristallographie, 2004, Vol 16, N°2.]
  		•  Calcite
    CaCO
     
    3
    Reference: [Clay Minerals, 23, 237{247. (2) (1990)]
  		•  Cancrinite
    Na
     
    6
    		Ca
     
    2
    		[(CO
     
    3
    		)
     
    2
    		|Al
     
    6
    		Si
     
    6
    		O
     
    24
    		] · 2H
     
    2
    		O
    Reference: []
  		•  Catapleiite
    Na
     
    2
    		Zr[Si
     
    3
    		O
     
    9
    		]·2H
     
    2
    		O
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa. ]
    Site Photo
    Los Archipelago (Los Islands), Guinea
    © Cristian B.
  		•  'Chlorite Group'
    Reference: [Clay Minerals, 23, 237{247. (2) (1990)]
  		•  Eudialyte
    Na
     
    15
    		Ca
     
    6
    		(Fe
    2+
     
    		,Mn
    2+
     
    		)
     
    3
    		Zr
     
    3
    		[Si
     
    25
    		O
     
    73
    		](O,OH,H
     
    2
    		O)
     
    3
    		(OH,Cl)
     
    2
    Reference: [Moreau, C., Ohnenstetter, D., Demaiffe, D., & Robineau, B. (1996). The Los Archipelago nepheline syenite ring-structure: a magmatic marker of the evolution of the central and equatorial Atlantic. Canadian Mineralogist, 34: 281-299. ]
    Site Photo
    Los Archipelago (Los Islands), Guinea
    © Cristian B.
  		•  Fluorite
    CaF
     
    2
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa. ]
  		•  Galena
    PbS
    Reference: []
  		•  Gibbsite
    Al(OH)
     
    3
    Reference: []
  		•  Grossular
    Ca
     
    3
    		Al
     
    2
    		[SiO
     
    4
    		]
     
    3
    Reference: []
  		•  Hastingsite
    [Na][Ca
     
    2
    		][Fe
    2+
    4
    		Fe
    3+
     
    		][(OH)
     
    2
    		|Al
     
    2
    		Si
     
    6
    		O
     
    22
    		]
    Reference: [Moreau, C., Ohnenstetter, D., Demaiffe, D., & Robineau, B. (1996). The Los Archipelago nepheline syenite ring-structure: a magmatic marker of the evolution of the central and equatorial Atlantic. Canadian Mineralogist, 34: 281-299. ]
  		•  Haüyne
    (Na,Ca)
     
    4-8
    		[Al
     
    6
    		Si
     
    6
    		(O,S)
     
    24
    		](SO
     
    4
    		,Cl)
     
    1-2
    Reference: []
  		•  'Hiortdahlite'
    (Ca,Na)
     
    3
    		(Zr,Ti)Si
     
    2
    		O
     
    7
    		(O,OH,F)
     
    2
    Reference: [Lacroix, A. (1924). Nouvelles observations sur les syénites néphéliniques des Iles de Los (Guinée). C. r. hedb. Séanc. Acad. Sci., Paris, 178, 1109-1114. ]
  		•  Illite
    K
     
    0.65
    		A
     
    2.0
    		 [][Al
     
    0.65
    		Si,
     
    3.35
    		O
     
    10
    		](OH)
     
    2
    Reference: [Clay Minerals, 23, 237{247. (2) (1990)]
  		•  Ilmenite
    Fe
    2+
     
    		TiO
     
    3
    Reference: []
  		•  IMA2008-024 (TL)
    (Ca,Na,REE,[])
     
    7
    		(Nb,Ti)[Si
     
    2
    		O
     
    7
    		]
     
    2
    		OF
     
    3
    Type Locality: Rouma Island (Roume; Roma; Ruma), Los Archipelago (Los Islands), Guinea
    Reference: [IMA website - Proposals approved in August 2008]
  		•  Kaolinite
    Al
     
    2
    		Si
     
    2
    		O
     
    5
    		(OH)
     
    4
    Reference: [Clay Minerals, 23, 237{247. (2) (1990)]
  		•  Kupletskite
    (K,Na)
     
    3
    		(Mn,Fe)
     
    7
    		Ti
     
    2
    		Si
     
    8
    		O
     
    26
    		(OH)
     
    4
    		F
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Låvenite
    (Na,Ca)
     
    2
    		(Mn
    2+
     
    		,Fe
    2+
     
    		)(Zr,Ti)[(O,OH,F)
     
    2
    		|Si
     
    2
    		O
     
    7
    		]
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
    Site Photo
    Los Archipelago (Los Islands), Guinea
    © Cristian B.
  		•  Leucophanite
    NaCaBeSi
     
    2
    		O
     
    6
    		F
    Reference: []
  		•  Löllingite
    FeAs
     
    2
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Magnetite
    Fe
    2+
     
    		Fe
    3+
    2
    		O
     
    4
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Microcline
    K[AlSi
     
    3
    		O
     
    8
    		]
    Reference: []
  		•  Molybdenite
    MoS
     
    2
    Reference: []
  		•  Muscovite
    KAl
     
    2
    		[(OH)
     
    2
    		|AlSi
     
    3
    		O
     
    10
    		]
    Reference: []
  		•  Nacareniobsite-(Ce)
    Na
     
    3
    		Ca
     
    3
    		(Ce,La,Nd)Nb[F
     
    3
    		|O|(Si
     
    2
    		O
     
    7
    		)
     
    2
    		]
    Reference: [G.C. Parodi and V. Chevrier : "New discoveries in nephelinites from Los island (Republic of Guinea)", 5th International Conference "Mineralogy & Museums", Paris, Sept. 5-8th 2004, Bull. de Liaison de la Soc. Franç. de Minéralogie et Cristallographie, 2004, Vol 16, N°2.]
  		•  Natrolite
    Na
     
    2
    		[Al
     
    2
    		Si
     
    3
    		O
     
    10
    		] · 2H
     
    2
    		O
    Reference: []
  		•  Nepheline
    (Na,K)[AlSiO
     
    4
    		]
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Normandite
    NaCa(Mn,Fe)(Ti,Nb,Zr)[(O,F)
     
    2
    		|Si
     
    2
    		O
     
    7
    		]
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Nosean
    Na
     
    8
    		[SO
     
    4
    		|Al
     
    6
    		Si
     
    6
    		O
     
    24
    		]
    Reference: []
  		•  Odinite (TL)
    (Fe,Mg,Al,Fe,Ti,Mn)
     
    2.4
    		(Si,Al)
     
    2
    		O
     
    5
    		(OH)
     
    4
    Type Locality: Los Archipelago (Los Islands), Guinea
    Reference: [Clay Minerals, 23, 237{247. (2) (1990)]
  		•  'Olivine'
    (Mg,Fe
    2+
     
    		)
     
    2
    		[SiO
     
    4
    		]
    Reference: []
  		•  Orthoclase
    K[AlSi
     
    3
    		O
     
    8
    		]
    Reference: []
  		•  Pyrite
    FeS
     
    2
    Reference: []
  		•  Pyrochlore
    (Ca,Na)
     
    2
    		Nb
     
    2
    		O
     
    6
    		(OH,F)
    Reference: []
  		•  Pyrophanite
    Mn
    2+
     
    		TiO
     
    3
    Reference: []
  		•  Pyrrhotite
    Fe
     
    7
    		S
     
    8
    		, (-4M), also given as Fe
     
    1-x
    		S (x = 0 - 0.2)
    Reference: []
  		•  Quartz
    SiO
     
    2
    Reference: [Clay Minerals, 23, 237{247. (2) (1990)]
  		•  Rinkite
    Ti(Na,Ca)
     
    3
    		(Ca,Ce)
     
    4
    		(Si
     
    2
    		O
     
    7
    		)
     
    2
    		OF
     
    3
    Reference: []
  		•  Rosenbuschite
    (Ca,Na)
     
    3
    		(Zr,Ti)[O|F|Si
     
    2
    		O
     
    7
    		]
    Reference: []
  		•  Sanidine
    K[AlSi
     
    3
    		O
     
    8
    		]
    Reference: []
  		•  Sérandite (TL)
    Na(Mn
    2+
     
    		,Ca)
     
    2
    		[HSi
     
    3
    		O
     
    9
    		]
    Type Locality: Rouma Island (Roume; Roma; Ruma), Los Archipelago (Los Islands), Guinea
    Reference: [Lacroix, A. (1931). Les pegmatites de la syénite sodalitique de l’île Rouma (archipel de Los, Guinée française). Description d’un noveau minéral (sérandite) qu’elles renferment. C. R. Acad. Sci. Paris, 192, 189-194. ]
  		•  'Smectite Group'
    A
     
    0.3
    		D
     
    2-3
    		[T
     
    4
    		O
     
    10
    		]Z
     
    2
    		·nH
     
    2
    		O
    Reference: []
  		•  Sodalite
    Na
     
    8
    		[Cl
     
    2
    		|Al
     
    6
    		Si
     
    6
    		O
     
    24
    		]
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Sodalite
    var: Hackmanite
    Na
     
    8
    		Al
     
    6
    		Si
     
    6
    		O
     
    24
    		(Cl
     
    2
    		,S)
    Reference: []
  		•  Sphalerite
    (Zn,Fe
    2+
     
    		)S
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Steacyite
    ([ ],K)(Na,Ca)
     
    2
    		(Th,U)[Si
     
    8
    		O
     
    20
    		]
    Reference: [Parodi, G. C., & Della Ventura, G. (1987). Steacyite from the Rouma Isle (Los Islands, Republic of Guinea). Neues Jarbuch fur Mineralogie, Mh., Jg. 1987, H. 5, 233-239]
  		•  Titanite
    CaTi[O|SiO
     
    4
    		]
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Villiaumite (TL)
    NaF
    Type Locality: Rouma Island (Roume; Roma; Ruma), Los Archipelago (Los Islands), Guinea
    Description: Found in small miarolitic cavities in nepheline syenites.
    Reference: [C.R.Acad.Sci. Paris (1908) 146, 213; Palache, Charles, Harry Berman & Clifford Frondel (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume II, John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124 pp.: 10.]
    Site Photo
    Los Archipelago (Los Islands), Guinea
    © 2007 Peter Cristofono
  		•  Vishnevite
    (Na,K)
     
    8
    		[(SO
     
    4
    		,CO
     
    3
    		)|Al
     
    6
    		Si
     
    6
    		O
     
    24
    		] · 2H
     
    2
    		O
    Reference: []
  		•  Wöhlerite
    NaCa
     
    2
    		(Zr,Nb)[(O,OH,F)
     
    2
    		|Si
     
    2
    		O
     
    7
    		]
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]
  		•  Zircon
    Zr[SiO
     
    4
    		]
    Reference: [Biagioni, C. (2007). I disilicati di Zr-Ti-Nb-REE delle sieniti a nefelina delle Iles de Los (Guinea). Tesi di laurea inedita, Università di Pisa.]


    63 entries listed. 54 valid minerals. 4 type localities (valid minerals).

    Localities in this Region:
    Guinea
     
    • Los Archipelago (Los Islands)

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