Oct 21 2013
Ettringite is a hydrous calcium aluminum sulfate mineral first described in 1874 from Ettringer Bellerberg, Germany. The mineral was named after its place of discovery.
Properties of Ettringite
The following are the key properties of Ettringite:
- Cell Data
- Space Group: P31c
- a = 11.23
- c = 21.44
- Z = 2
- Crystal Data
- Hexagonal
- Point Group: 3m
- Crystals prismatic and striated along [0001], to 20 cm, commonly unterminated, rarely dipyramidal {1012}; fibrous to cottonlike
- X-ray Powder Pattern: 9.73 (100), 5.61 (80), 3.88 (50), 2.564 (45), 2.209 (45), 2.773 (40), 4.69 (35)
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
| H2O |
46.3 |
45.93 |
| CaO |
26.6 |
26.81 |
| SO3 |
18.8 |
19.14 |
| Al2O3 |
7.0 |
8.12 |
| CO2 |
0.8 |
- |
| Total |
99.5 |
100.00 |
- Optical Properties
- Optical Class: Uniaxial (–), changing to uniaxial (+) on dehydration
- ω = 1.464
- ε = 1.458
- Estimated Properties
| Electron density |
Bulk density (electron density)=1.89 g/cm3
note: Specific gravity of Ettringite =1.80 g/cm3 |
| Photoelectric |
PEEttringite = 2.97 barns/electron
U= PEEttringite x ρElectron density= 5.60 barns/cm3 |
| Fermion index |
Fermion index = 0.001
Boson index = 0.998 |
| Radioactivity |
Ettringite is not radioactive |
How to Identify Ettringite
Ettringite is either colorless or white in color. It is transparent in appearance and non-magnetic. The mineral is non-fluorescent with white streak, perfect cleavage and vitreous luster. It forms needle-like crystals. The hardness of ettringite ranges from 2 to 2.5, and its density is 1.8 g/cm3.
Global Distribution
Ettringite is distributed in the following places:
- Ettringer-Bellerberg volcano, near Mayen, and Schellkopf near Brenk, Eifel district, Germany
- Zeilberg quarry, Maroldsweisach, Bavaria
- Boisséjour, near Clermont-Ferrand, Puy-de-Dôme, France
- Scawt Hill, near Larne, Co. Antrim, Ireland
- Hatrurim Formation, Israel
- N’Chwaning mine, Kuruman district, Cape Province, South Africa
- Crestmore quarry, Riverside Co., California
- Lucky Cuss mine, Tombstone, Cochise Co., Arizona
Occurrence of Ettringite and Useful Mineral Association
Ettringite occurs in xenoliths or metamorphosed limestone near igneous contacts. It also occurs as weathering crusts on larnite rocks.
The minerals that are closely associated with ettringite include gypsum, mayenite, hydrocalumite, afwillite, hydrocalumite and portlandite.
References