Samuelsonite
General
Category	Phosphate minerals
Formula (repeating unit)	(Ca,Ba)Ca8Fe22+Mn22+Al2[(OH)2(PO4)10]
IMA symbol	Sms[1]
Strunz classification	8.BF.10
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Unit cell	a= 18.495 Å, b= 6.805 Å c= 14.000 Å, β= 112.75°; Z = 2
Identification
Color	Pale yellow
Crystal habit	Prismatic crystals, elongated and striated
Cleavage	Fair on {001}
Mohs scale hardness	5
Luster	Adamantine, Sub-Adamantine
Streak	White
Diaphaneity	Transparent
Specific gravity	3.353
Optical properties	Biaxial (+)
Refractive index	nα = 1.645 - 1.648 nβ = 1.650 - 1.655 nγ = 1.655 - 1.667
Birefringence	0.0100-0.0190
References	[2][3][4]

Samuelsonite is a complex mineral that is found near North Groton, Grafton County, New Hampshire, US. Additionally, it is most commonly found as a secondary mineral in granite pegmatite. Samuelsonite is named after Peter B. Samuelson,^[2] a prospector from Rumney, New Hampshire.

The mineral has a pale yellow color and has a hardness of 5 on Mohs scale.^[3] The crystal is generally yellow, flat, and with straited crystals and blue trolleites.^[5] Samuelsonite is monoclinic. There are three vectors of unequal length in this crystal system. The three vectors form a rectangular prism with a parallelogram at the base. Therefore, two of the vectors are perpendicular, while the third makes an angle that is not equal to 90°.^[6] Samuelsonite has biaxial birefringence (trirefringence), meaning when light passes through the optic axis it is split into two rays due to the difference in refractive index of the ray with parallel polarized light compared to the ray with perpendicular polarized light.

References