Synchysite-(Ce): CaCe(CO3)2F
Synchysite-(Nd): CaNd(CO3)2F
Synchysite-(Y): CaY(CO3)2F
Anhydrous carbonates containing halogen, synchysite group
Specific gravity: Ce 3.9; Synchysite-(Y) 3.89 to 4.1; Synchysite-(Nd) 4.21
Hardness: Synchysite-(Ce) 4½; Synchysite-(Y) 6 to 6½; Synchysite-(Nd)
Streak: Synchysite-(Ce) and synchysite-(Nd) White; Synchysite-(Y) Light brown
Synchysite-(Ce) Grey, grey-yellow, orange-yellow, brown, beige, light green, white
Synchysite-(Y) White, reddish brown, greyish yellow, dull yellow; colourless to light yellow in transmitted light
Synchysite-Nd) Rose-pink, Pale grey-blue, light grass-green; pale violet to colourless in transmitted light
Solubility: Synchysite-(Y) and synchysite-(Ce) are readily soluble in acids

Hydrothermal environments

Synchysite-(Ce) is best known from alpine fissure-type veins in granite and alkalic syenite, where it is typically accompanied by other rare-earth minerals and quartz, albite, the TiO2 paramorphs and chlorite. It is found with parisite in rare-earth-bearing pegmatites and it also occurs in carbonatites (Webmin, HOM, MW ).
Synchysite-(Y) occurs in pegmatites, in carbonatites and in alpine fissure-type veins, where it is typically accompanied by other rare-earth minerals and quartz, albite, the TiO2 paramorphs and chlorite (HOM, MW).


At the Francon quarry, Montreal, Quebec, Canada, synchysite-(Ce) is the commonest of the rare-earth minerals found in the quarry, but still it is very rare. Associated minerals include quartz, fluorite, dawsonite, marcasite, pyrite, mordenite, calcite, celestine and baryte (Minrec 37.1.47 ).

At the Holičky deposit, Stráž, Česká Lípa District, Liberec Region, Czech Republic, synchysite-(Nd) is an authigenic mineral occuring as microcavity fillings in sandstone-type uranium deposits. Associated minerals include florencite-(La), sphalerite, manganoan siderite, pyrite, kaolinite and chalcedony (HOM, Dana).

At its type locality, the Narssârssuk pegmatite, Narsaarsuk Plateau, Igaliku, Kujalleq, Greenland, Denmark, synchysite-(Ce) occurs in a syenite pegmatite associated with astrophyllite, catapleiite, neptunite, epididymite, elpidite, cordylite-(Ce), fluorite, rhodochrosite, polylithionite, aegirine, microcline and albite (HOM, Dana, Mindat).

At the Trimouns quarry, France, synchysite-(Ce) is commonly associated with allanite, and rarely with xenotime. It may form syntaxic intergrowths with bastnäsite (MinRec 35.3.242).

At its type locality, the Grebnik mountain, Klina, District of Peja, Kosovo, synchysite-(Nd) occurs in limestone at the base of the deposit (Dana, HOM, AM 64.658).

At the Khibiny massif, Russia, synchysite-(Ce) is associated with ewaldite, belovite-(Ce), fluorite, nenadkevichite, ancylite-(Ce), kukharenkoite-(Ce), mckelveyite-(Y), burbankite, calcite, baryte and orthoclase (HOM).

At Piz Blas, Val Naps, Graudunden, Switzerland, synchysite-(Ce) occurs with gadolinite, K-feldspar variety adularia and xenotime in alpine veins (Dana).

At Beddgelert Forest, Beddgelert, Gwynedd, Wales, UK, synchysite-(Y) has been found in altered rhyolite as radiating sheaves intergrown with quartz and K-feldspar (MW).

At Cwmorthin Quarry, Blaenau Ffestiniog, Gwynedd, Wales, UK, synchysite-(Ce) is rare, but a small number of specimens have been recovered from alpine fissure-type veins hosted by banded tuff - turbidite. Associated minerals include quartz, anatase and xenotime (MW).

At Gloddfa Ganol Quarry, Blaenau Ffestiniog, Gwynedd, Wales, UK, synchysite-(Ce) is very rare, occurring in alpine fissure-type quartz veins and, with albite and anatase, in occasional blocks of vuggy brecciated slate; it is often sparingly coated in microscopic crystals of pyrite (MW).

At Manod Quarry, Blaenau Ffestiniog, Gwynedd, Wales, UK, synchysite occurs in association with quartz and albite in alpine fissure-type veins cutting an altered intermediate intrusive rock (MW).

At Tanygrisiau Station, Blaenau Ffestiniog, Gwynedd, Wales, UK, synchysite-(Ce) was found as a very rare late-stage mineral in the alpine fissure-type veins that were exposed by blasting in the mid-1970s. Associated minerals included quartz, albite, anatase and clinochlore (MW).

At the Dolyhir Quarry, Old Radnor, Powys, Wales, UK, synchysite-(Ce) has been found in alpine-type fractures cutting shale immediately below an unconformity (MW).

At the Henry pegmatite, Cotopaxi, Colorado, USA, synchysite-(Ce) and and synchysite-(Y) are associated with kainosite-(Y) (Dana,AM 47.337-343).

At Quincy, Massachusetts, USA, synchysite-(Ce) occurs with parisite (Dana).

At Dover, Morris county, New Jersey, USA, synchysite-(Y) is associated with kainosite-(Y), bastnäsite, xenotime, hematite and quartz (HOM).

At its type locality, the Scrub Oak Mine, Mine Hill Borough, Morris county, New Jersey, USA, synchysite-(Y) occurs in aggregates mixed with xenotime, hematite and quartz. Most of the aggregates have rims of bastnäsite (AM 45.92-98).
Synchysite-(Ce) also occurs at the Scrub Oak mine, intimately intergrown with quartz, xenotime, bastnäsite and hematite (Dana).

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