Scapolite

scapolite

diopside

titanite

zircon

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Scapolite is a series between
Marialite Na₄Al₃Si₉O₂₄Cl
and
Meionite Ca₄Al₆Si₆O₂₄(CO₃)
These are tectosilicates (framework silicates)
Crystal System: Tetragonal
Specific gravity: 2.5 to 2.62 measured 2.54 calculated marialite
2.74 to 2.78 measured 2.86 calculated meonite
Hardness: 5 - 6½
Streak: White
Colour: Colourless, white, grey, yellow, green, blue, red to violet
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Volcanic igneous environments
Pegmatites
Carbonatites
Metamorphic environments
Hydrothermal environments

Scapolite is characteristic in limestone as a contact metamorphic mineral. It also occurs in regionally metamorphosed rocks. It is common in a wide variety of ore deposits, particularly skarn. It is also present in hydrothermally altered basic igneous rocks. Marialite is commonly associated with very high NaCl in hydrothermal fluids (AofA).
Scapolite may occur in schist and gneiss.
It is associated with diopside, amphibole, garnet, apatite, titanite and zircon.
Scapolite is a mineral of the amphibolite and granulite facies, but it has also been reported in rocks from the greenschist, eclogite and sanidinite facies. (DHZ 4 p 331).

Localities

In the Mount Lofty Ranges of South Australia, scapolite is associated with calcite, K-feldspar and pyroxene (DHZ 4 p332).

At lots 10 and 11 of concession 1, Bathurst Township, Lanark County, Ontario, Canada (DeWitts corner), the deposit is located in the Grenville Geological Province, which consists mostly of marble, gneiss, and quartzite. Syenite-migmatite was also reported in the area where the vein-dikes are located. Characteristic features of the vein-dikes include the fact that perfectly formed euhedral crystals of different minerals can often be found floating in calcite with no points of contact with the walls. Sometimes these crystals have inclusions of calcite, irregular or rounded in shape. It has been argued that at least some of the vein-dikes were formed as a result of melting of Grenville marble.
Scapolite occurs as pale yellow-brown, short-prismatic crystals to 3 mm that form aggregates with 1 to 2 mm green diopside crystals (R&M 97.6.556-564).

At Craigmont, Renfrew county, Ontario, Canada, scapolite occurs in nepheline gneiss, associated with nepheline, corundum and plagioclase (DHZ 4 p333).

At the Spain mine, Griffith township, Renfrew county, Ontario, Canada, orthoclase pseudomorphs after scapolite have been found (KL p263).

At Långö, Finland, scapolite occurs in a pegmatite dyke associated with biotite, allanite, quartz, fluorite, calcite and apatite (DHZ 4 p334).

At Arendal, Aust-Agder, Norway, scapolite occurs with epidote (FM OP 167).

In Yakutia, Russia, scapolite is associated with diopside, hornblende, garnet and tourmaline (DHZ 4 p334).

At Loos, Sweden, scapolite occurs in pegmatite dykes, and at the contact between the dykes and limestone, associated with albite, plagioclase, diopside, wollastonite, pargasite, grossular and fluorite, commonly intergrown with diopside or quartz (DHZ 4 p331).

Amity, Town of Warwick, Orange county, New York, USA, is an area of granite intrusions into marble and associated gneiss. The marble is mostly composed of white crystalline calcite that often has small flakes or spheres of graphite and phlogopite. Scapolite occurs as large, white to pale grey crystals to 30 cm in clusters to 60 cm. It is usually associated with augite and often fluoresces dark crimson red. Most of the scapolite appears to be near the mid-point of the meionite-marialite series, but scapolite from one of the excavations was found to be near end-member marialite and fluoresces bright yellow under longwave ultraviolet light. Most scapolite crystals from this locality are altered on their surfaces. Alteration ranges from chlorite penetrating into small fractures to wholesale alteration of the outer rind to a replacement texture of albite and muscovite within a matrix of chlorite (R&M 96.5.439).

At French Creek, Pennsylvania, USA, scapolite is intergrown with prehnite and associated with heulandite, chlorite, titanite, apatite and epidote, an assemblage which may have formed under zeolite facies conditions (DHZ 4 p331).

Alteration

In many cases scapolite is derived by alteration from plagioclase feldspar.

anorthite and CO₂ to meionite (scapolite series), corundum and quartz
4Ca(Al₂Si₂O₈) + CO₂ ⇌ Ca₄Al₆O₂₄(CO₃) + Al₂O₃ + 2SiO₂ (DHZ 4 p334).

anorthite and calcite to meionite (scapolite series)
3Ca(Al₂Si₂O₈) + CaCO₃ ⇌ Ca₄Al₆O₂₄(CO₃)
This reaction occurs in the presence of a high CO₂ pressure in an environment deficient in (Al+Na+K) (DHZ 4 p331).

meionite (scapolite series) and H₂O to clinozoisite and CO₂
Ca₄Al₆O₂₄(CO₃) + H₂O ⇌ 2Ca₂Al₃Si₃O₁₂(OH) + CO₂ (DHZ 4 p334).

meionite (scapolite series) and augite to garnet, calcite and quartz
Ca₄Al₆O₂₄(CO₃) + 3Ca(Mg,Fe²⁺)Si₂O₆ ⇌ 3Ca₂(Mg,Fe²⁺)Al₂(SiO₄)₃ + CaCO₃ + 3SiO₂ (DHZ 4 p334).

meionite (scapolite series), calcite and quartz to grossular and CO₂
Ca₄Al₆O₂₄(CO₃) + 5CaCO₃ + 3SiO₂ ⇌ 3Ca₃Al₂(SiO₄)₃ + 6CO₂ (DHZ 4 p334).

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