Monazite-(La)

 IMA-GP
Thorium 38.4.3.2
(Dana Classification Number)
(No Images) 7/A.15-10
(Strunz ID)

Property Data Remarks
Named for: From the Greek word monazeis, "to be alone", in allusion to its isolated crystals and rarity when first found, and its Lanthanum (rare earth) content
Alternate
    Name(s):
  • Monazite
    		•  Used as a collective name for all Monazite minerals
    Mineral Class:
    Phosphates, Arsenates and Vanadates
      Waterfree phosphates [PO4]-3 without unfamiliar anions, cations of very big size: Ca, Na and related cations
        Monazite group
    		 
    Chemical
        Formula:    		 (La, Ce, Nd, Th)PO4  
    Chemical
        Composition:
    Cerium: (Ce) 14.60%
    Lanthanum: (La) 28.95%
    Neodymium: (Nd) 12.02%
    Oxygen: (O) 26.68%
    Phosphorus: (P) 12.91%
    Thorium: (Th) 4.84%
    		by weight
    Molecular
        Weight:    		 239.90 daltons (amu)
    Specific
        Radioactivity:

    (All radiation is for a 1 gram, fully aged specimen)

    Specific Activity Dose Rate
    Becquerels Curies milliRems/hour microSieverts/hour
    2.167 × 1003 5.86 × 10-08 0.03 3.01

    Estimated Average Annual Exposure: 360 mRem (3.6 milliSieverts)
    Crystalography:
    System: Monoclinic - Prismatic
    Axial Ratios: a: 0.9686
    b: 1
    c: 0.9215
    Cell Dimensions: a: 6.79 Å
    b: 7.01 Å
    c: 6.46 Å
    Z: 4
    b: 103.633°
    V: 298.82 Å3
    DenCalc: 5.33
    H-M Symbol: 2/m
    Space Group: P21/n
    X-Ray Diffraction:
      By Intensity ( I/Io )    		 (1): 3.12 Å
    (0.85): 3.31 Å
    (0.4): 2.15 Å
    		Monazite-(La)
    Crystal
    Habit:
  • Crystalline - Fine
  • Twinning common - Crystals are usually twinned
  • Crystal surfaces are often etched and pitted
    		•   
    Cleavage:
    [001] Distinct
    [010]  
    [100] Indistinct

    Cleavage often results in shards or acutely angled splinters
    Metamictation will eliminate cleavage
    A basal parting direction is sometimes noticeable

    		  
    Fracture:
  • Conchoidal

    • Metamictation increases the degree of conchoidal fracture.    		  
    Moh's
        Hardness:    		 5 - 5.5  
    Density: 4.8 - 5.5 grams/cm3
    Color: Dark brown, Brown, Yellowish brown, Redish brown, Pink, or Yellow  
    Streak: Grayish white  
    Luster: Adamantine - Resinous  
    Diaphaneity: Transparent to Subtranslucent  
    Pleochroism:
    (x):  
    (y:)  
    (z:)  
    		 
    Ultra Violet
        Fluorescence:
    Long Wave:  
    Short Wave:  
    		 
    Magnetism: Non-magnetic  
    Occurance:
    • In phosphate pegmatites as solitary crystals
    • An accessory mineral in granite, syenite and gneiss
    • In beach and river placer deposits
    • A trace constituent in many ordinary igneous, metamorphic and vein filling rocks
    		  
    Associated
        Minerals:

    Arsenopyrite, Bismuthinite, Bismutite, Bornite, Brochantite, Calcite, Cassiterite, Chrysocolla, Copper, Ferberite, Fluorapatite, Goethite, Jarosite, Kaolinite, Molybdenite, Monazite-(Ce), Muscovite, Plumbogummite, Pyrite, Pyromorphite, Pyrrhotite, Quartz, Rhodochrosite, Scheelite, Siderite, Sphalerite

    Mineral   -   > 50% of sites
    Mineral   -   > 25% of sites
    Mineral   -   > 15% of sites
    Minerals   -   Uranium & Thorium
    mineral links

    Locations:

    Rare

    Monazite-(La) Locations
    Notes:

    Radioactive, often strongly so. This can cause crystals to be metamic.

    Monazite is technically four different minerals. Because of a lack of any great difference between them they are often considered as one mineral, 'Monazite'. The four Monazites have different chemical makeup reflected in their respective names, and different crystaline forms.