Jun 5 2014
Macdonalite is a rare barium silicate mineral, which was first discovered in 1965 from Big Creek - Rush Creek sanbornite deposit, Fresno Co. California.
It was named for Gordon Andrew Macdonald, an American volcanologist at the University of Hawaii.
Properties of Macdonaldite
The following are the key properties of Macdonaldite:
- Cell Data
- Space Group: Bmmb; B2mb; or Bm21b
- a = 14.06(1)
- b = 23.52(2)
- c = 13.08(1)
- Z = 4
- Crystal Data
- Orthorhombic
- Point Group: 2/m 2/m 2/m or mm2
- Needle-like crystals show {010}, {001}, and {100}, and are elongated along [100], to 6mm; also fibrous, in radiating aggregates, and granular
- X-ray Powder Pattern: 6.5 (100), 4.36 (80), 6.3 (50), 3.36 (50), 3.02 (45), 2.74 (45), 8.9 (40)
- Chemical Composition
| Elements |
Content |
| SiO2 |
61.1 |
| CaO |
14.8 |
| LOI |
13.7 |
| BaO |
10.2 |
| MgO |
<6.05 |
| Al2O3 |
0.06 |
| SrO |
<0.05 |
| TiO2 |
0.01 |
| FeO |
<0.01 |
| MnO |
0.004 |
| Total |
[100.00] |
- Optical Properties
- Optical Class: Biaxial (+) or (-)
- Orientation: X = c; Y = b; Z = a
- α = 1.518(2)
- β = 1.524(2)
- γ = 1.530(2)
- 2V(meas.) = 90(5)°
- 2V(calc.) = 90°
- Estimated Properties
| Electron density |
Bulk density (electron density) = 2.35 g/cm3
note: Specific gravity of Macdonaldite = 2.36 g/cm3 |
| Photoelectric |
PEMacdonaldite = 38.38 barns/electron
U = PEMacdonaldite x ρElectron density = 90.28 barns/cm3 |
| Fermion index |
Fermion index = 0.02
Boson index = 0.98 |
Radioactivity
|
Macdonaldite is not radioactive
|
How to Identify Macdonaldite
Macdonaldite is a transparent, colorless or white mineral, having perfect cleavage, vitreous luster, and white streak. It forms needle-like crystals.
The hardness of macdonaldite ranges from 3.5 to 4, and its density is 2.27 g/cm3.
Global Distribution
Macdonaldite is widely distributed in the following places:
- Big Creek-Rush Creek area, Fresno Co.
- Trumbull Peak, near Incline, Mariposa Co. California, USA
Occurrence of Macdonaldite and Useful Mineral Association
Macdonaldite is disseminated in a sanbornite-quartz-bearing metamorphic rock, and occurs as fracture coatings and veinlets.
It is closely associated with quartz and sanbornite.
References