| Paragonite | |
|---|---|
 Paragonite withgarnet | |
| General | |
| Category | Phyllosilicateminerals, dioctahedralmicagroup |
| Formula | NaAl2(AlSi3O10)(OH)2 |
| IMA symbol | Pg[1] |
| Strunz classification | 9.EC.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-M symbol) |
| Space group | C2/c |
| Identification | |
| Color | Colorless, pale yellow, grayish, grayish white, greenish, light apple-green |
| Crystal habit | massive, fibrous or scaly |
| Twinning | common on the [310] less common on the {001} |
| Cleavage | Perfect on the {001} |
| Fracture | Micaeous |
| Tenacity | Elastic |
| Mohs scale hardness | 2.5–3 |
| Luster | Pearly |
| Streak | White |
| Diaphaneity | transparent to translucent |
| Specific gravity | 2.78 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.564 – 1.580 nβ = 1.594 – 1.609 nγ = 1.600 – 1.609 |
| Birefringence | δ = 0.036 |
| Dispersion | r < v strong |
| Ultravioletfluorescence | None |
| References | [2][3][4][5] |
Paragonite is amineral, related tomuscovite. Itsempirical formula isNaAl2(AlSi3O10)(OH)2. A widesolvus separates muscovite from paragonite, such that there is littlesolid solution along the vector[clarification needed]Na+K+ and apparentmicas of intermediate composition is most commonly a microscopic (or even sub-microscopic) intergrowth of two distinct micas, one rich in K, and the other in Na. Paragonite is a common mineral in rocksmetamorphosed underblueschist facies conditions along with other sodic minerals such asalbite,jadeite andglaucophane. During the transition from blueschist togreenschist facies, paragonite andglaucophane are transformed intochlorite and albite.[6] Jadeite bearingpyroxene minerals have suggestedclinozoisite and paragonite are associated and derived fromlawsonite releasingquartz and water via the following reaction:[7]
It was first described in 1843 for an occurrence at Mt. Campione,Tessin,Switzerland.[4] The name derives from theGreek,paragon, formisleading, due to its similar appearance totalc.[5]
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