Hotsonite

Hotsonite is a mineral whose name derives from the farm Hotson 42, located 65 km west of the town of Pofadder, in Bushmanland, northwestern Cape Province, South Africa. This is an arid region with an average rainfall of 3 inches per annum. The name was approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association (July 1983)^[5] It is chemically related to sanjuanite and kribergite.

Hotsonite
General
Category	Phosphate minerals, sulfate minerals
Formula	Al11(PO4)2(SO4)3(OH)21.16H2O
IMA symbol	Hot[1]
Strunz classification	08.DF.05
Dana classification	43.05.18.01
Crystal system	Triclinic
Space group	1
Unit cell	a= 0.9631, b= 1.0, c= 0.9048
Identification
Color	White
Crystal habit	Compact
Fracture	Earthy
Mohs scale hardness	2.5
Luster	Silky
Streak	White
Diaphaneity	Transparent
Specific gravity	2.06
Density	2.060-2.068
Refractive index	Less than 0.003
Other characteristics	Sometimes weakly fluorescent under SW and LW UV
References	[2][3][4][5]

Discovery and occurrence

Hotsonite was discovered while investigating for aluminous metamorphic rocks in an abandoned sillimanite quarry in 1982. The two senior authors sampled peculiar veins and encrustations of cryptocrystalline fine-grained white material. One of the materials had properties which could not be matched to any known mineral.

The mineral occurs closely with zaherite, Al₁₂(SO₄₎₅(SO₄₎₃(OH)₂₆.20H₂O.^[5]

Physical properties

Hotsonite's physical properties are similar to other hydrated aluminous sulfates and some phosphates. It occurs as a white chalk like mineral with a dull to silky luster, and an earthy fracture. When observed under magnification of 500 times, it has a flaky appearance. Hotsonite appears with a white coloration, and small grain size. The Mohs hardness is 2.5, and with a density value of 2.060 to 2.068.^[5]

Chemical composition

The chemical analysis was carried out using X-ray fluorescence, and the water was calculated by the Penfield method.

Oxide	wt %
SiO2	0.35
Al2O3	39.15
Fe2O3	0.03
MgO	0.28
CaO	0.24
Na2O	0.21
K2O	0.00
P2O5	9.85
SO3	16.80
H2O	33.30
Total	100.21
[5]

Diffraction information

Powder diffraction used for hotsonite data:

d(obs)	d(calc)	(hkl)	l/l
10.05	10.05	010	100
8.45	8.42	11-1	40
6.13	6.11	011	1
5.48	5.50	111	1
5.20	5.19	11-2	10
5.01	5.03	020	10
4.97	4.97	1-1-1	2
4.77	4.76	20-1	2
4.63	4.64	10-2	20
4.43	4.43	220	10
4.34	4.34	21-2	7
3.91	3.91	012	7
3.67	3.67	2-1-1	10
3.62	3.63	2-11	2
3.46	3.46	1-2-1	6
3.30	3.31	22-3	1
3.13	3.14	33-2	3
3.08	3.08	311	2
2.97	2.97	30-2	1
2.87	2.87	24-1	2
2.83	2.83	12-2	2
2.75	2.75	222	1
2.68	2.68	34-1	1
2.58	2.60	22-4	1
2.56	2.56	04-2	1
2.47	2.47	430	1
2.41	2.41	411	1
2.34	2.34	241	1
2.32	2.32	20-4	1
2.28	2.28	2-32	1
2.25	2.25	344	1
2.23	2.23	35-1	1
2.17	2.17	511	1
2.14	2.14	303	1
2.11	2.11	510	1
2.06	2.06	41-4	1
2.01	2.01	050	1
1.984	-	-	1
1.944	-	-	2
1.921	-	-	1
1.900	-	-	1
1.867	-	-	1
1.844	-	-	1
1.782	-	-	3
1.687	-	-	1
1.682	-	-	1
1.665	-	-	1
1.585	-	-	2
1.539	-	-	1
1.526	-	-	1
1.495	-	-	1
1.462	-	-	1
1.449	-	-	1
1.407	-	-	1
1.378	-	-	1
1.368	-	-	1
[5]