Secondary names

Allenite

IMA Code

Phy

	Formula	Name	Family	Number min-max	Isotope mole fraction	State	Relevance
	$Mg^{2+}$	Magnesium(II) cation	element	1		constituent cation	main
	$(SO_4)^{2-}$	Sulfate anion	chemical function	1		anionic radical	main
	$H_2O$	Water	molecule	5		hydration	main

Composition comments

common impurities: Fe, Mn, Ni, Ca

Chemical functions

	Function	Number
	$(SO_4)^{2-}$	1
	$R-OH$	2

Chemical bonds

	Bond	Number
	$\cdot Mg^{2+} \cdot O^{-}-$	2
	$-O \dots H-$	10
	$-O-H$	2
	$\dddot - \dddot - \dddot - S \dddot - O^{-1/2}$	4

Oxides

Formula	$MgO$	$SO_{3}$	$H_{2}O$
Mass fraction (%)	19.15	38.05	42.8

Strunz

Class

sulfates - chromates - molybdates - tungstates (07)

Division

sulfates (selenates, etc.) without additional anions, with H2O (07.C)

Family

with only medium-sized cations (07.CB)

Code

07.CB.20

Dana

Major class

sulfates, chromates, selenates (VI)

Class

hydrated acid and sulfates (29)

Type

where AXO4.x(H2O) (29.06)

Group

Chalchanthite group (Pentahydrates, triclinic: P-1) (29.06.07)

Code

29.06.07.03

Phase type

crystalline

Crystal system

triclinic

Crystal class

pinacoidal

Crystal class symbol

-1 (Ci)

Crystal spacegroup

P-1

Refringence type

biaxial

Refringence sign

negative

Birefringence

0.011 - 0.023

Refraction index $n_{\alpha}$

1.482 - 1.495

Refraction index $n_{\beta}$

1.492 - 1.512

Refraction index $n_{\gamma}$

1.493 - 1.518

Pure color

colorless

Color

colorless, white, light blue, light greenish blue

Diaphaneity

transparent to translucent

Luster

vitreous

Links

• Wikipedia: Pentahydrite
• SaltWiki: Pentahydrite
• Webmineral: Pentahydrite
• Mindat: Pentahydrite
• Handbook of Mineralogy (Min. Soc. Am): Pentahydrite