Formula: (Mn2+,Mg,Al)3(Si,Al)2O5(OH)4
Phyllosilicate (sheet silicate), serpentine subgroup of the kaolinite-serpentine group
Specific gravity: 3.07
Hardness: 2½
Streak: Yellowish white
Colour: Yellow

Metamorphic environments

Kellyite is a rare manganese mineral.

At Mont Saint-Hilaire, Canada, kellyite occurs in an intrusive alkalic gabbro - syenite complex, associated with aegirine, analcime, calcite, catapleiite, microcline and natrolite (HOM).

At the type locality, the Bald Knob deposit, Sparta, Alleghany county, North Carolina, USA, kellyite occurs in a metamorphic manganese deposit with other manganese silicates (Webmin, Dana). Associated minerals include kutnohorite, galaxite, jacobsite, manganoan chlorite, alleghanyite, sonolite and tephroite (HOM, Dana, AM 59.1153-1156).

Common impurities: Ti,Fe,H2O

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