Lansfordite

Lansfordite is a mineral of magnesium carbonate (MgCO
₃). It represents the pentahydrate of magnesium carbonate, and has the total formula MgCO₃·5H₂O .^[2] Landsfordite was discovered in 1888 in a coal mine in Lansford, Pennsylvania. It crystallizes in the monoclinic system (space group P2₁/c^[3]) and typically occurs as colorless to white prismatic crystals and stalactitic masses.^[4] It is a soft mineral, Mohs hardness of 2.5, with a low specific gravity of 1.7. It is transparent to translucent with refractive indices of 1.46 to 1.51.^[5] The mineral will effloresce at room temperature, producing nesquehonite.^[6]

Lansfordite
General
Category	Carbonates
Formula	MgCO3·5H2O
IMA symbol	Lfd[1]
Strunz classification	5/D.01-30
Dana classification	15.1.6.1
Crystal system	Monoclinic
Space group	P21/c (No. 14)
Unit cell	a=7.3458 Å, b=7.6232 Å, c=12.4737 Å, β=101.722°
Identification
Formula mass	174.39
Colour	Colourless, white after exposure
Crystal habit	Crystals, stalactites terminated by crystal faces, efflorescences, parallel growths.
Cleavage	Perfect, Distinct
Mohs scale hardness	2.5
Luster	Vitreous (if fresh)
Streak	White
Diaphaneity	Translucent, opaque after exposure
Specific gravity	1.6
Density	1.6
Birefringence	0.042