1. Pyroxenoid Group XNSiNO3N
X is a large-radius divalent cation, typically Ca, Mn, or Fe. The symmetry is usually triclinic and results from a mismatch between the sizes of the divalent cation and the silicate chain. The repeat integer n, increases as the mean size of the divalent cation decreases. For wollastonite and bustamite, n = 3, for rhodonite, n = 5, for pyroxmangite and pyroxferroite, n = 7, and for ferrosilite III, n = 9. In addition to the above anhydrous proxenoids, there is also a series of hydrous pyroxenoids in which Na + H substitute for one of the divalnet cations giving us pectolite (NaHCa2Si3O9) and serandite (NaHMn2Si3O9).
From
Presentation prepared by Oliver Boyd

2. Pyroxenoid End Members
Bustamite
N = 3
Wollastonite
Rhodonite
N = 5
Pyroxferrite
N = 7
Pyroxmangite
Ferrosilite III
N = 9
Formula
Mn2+2.25Ca0.75
Si3O9
Ca3
Mn3+0.6Fe2+0.2
Mg0.1Ca0.1
SiO3
Fe2+6Mn2+
4(Si7)O21
Fe2+Mn2+6
Fe2+18
Si18O27
Crystal System
Triclinic -1
P-1 a
15.46
7.94
6.68
6.632
6.721
6.628 b
7.18
7.32
7.66
7.563
7.467 c
13.84
7.07
12.22
17.38
22.607 
89.567
90.033
111.1
114.31
113.17
115.32 
94.883
95.367
86.016
82.75
82.27
80.56 
93.203
94.58
94.13
95.49 Z 12 6 10
1.2 18
Volume (Å3)
397.92
581.04
785.58
802.71
997.2
Density (kg/m3)
5100
2910
3620
3840
3740
3950
From

3. Pyroxenoid Occurrences
Ferrosilite: Found in basic and ultrabasic igneous rocks.
Bustamite: In manganese ores formed by metamorphism of manganese-bearing sediments with attendant metasomatism.
Rhodonite: Hydrothermal, metamorphic and, metasomatic rocks.
Pyroxferrite: Gabbroic rocks. Forms a series with pyroxmangite.
Pyroxmangite: Metamorphic and contact metasomatism of Mn-bearing rocks. Forms a series with pyroxferroite

4. Pyroxenoid Uses
Wollastonite: Wollastonite is an industrially important mineral. It is a necessary ingredient in heat-resistant refractory ceramics and is used as a filler in paint. It is also used in the manufacture of paper and plastics.
Rhodonite: Rhodonite is a popular mineral among collectors. It is also a minor gemstone, being cut and polished into cabochons, beads, and other ornamental objects. Rhodonite is also a minor ore of manganese.

5. Pyroxenoid: Bustamite
Physical Properties
Cleavage: [100] Perfect, [110] Good, [110] Good
Color: brown red, light pink, or pink.
Density: , Average = 3.37
Diaphaniety: Transparent to Translucent
Hardness:
Luminescence: Fluorescent.
Luster: Vitreous (Glassy)
Streak: white
Optical Properties
Optical Data: Biaxial (-), a= , b= , g= , birefringence=
Pleochroism (x): colorless.
Pleochroism (y): colorless.
Pleochroism (z): colorless.
From

6. Pyroxenoid: Wollastonite
Physical Properties
Cleavage: [100] Perfect, [102] Good, [001] Good
Color: white, yellow, gray, red, or brown.
Density: , Average = 2.84
Diaphaniety: Subtransparent to translucent
Hardness: 5 - Apatite
Luminescence: Fluorescent.
Luster: Vitreous - Silky
Streak: white
Optical Properties
Optical Data: Biaxial (-), a= , b= , g= , birefringence= , 2V(Calc)=44-50, 2V(Meas)=40. Dispersion r > v distinct.
Pleochroism (x): colorless.
Pleochroism (y): colorless.
Pleochroism (z): colorless.
From

7. Pyroxenoid: Rhodonite
Physical Properties
Cleavage: [110] Perfect, [110] Perfect
Color: pink, rose red, brownish red, black, or yellow.
Density: , Average = 3.6
Diaphaniety: Transparent to translucent
Hardness: 6 - Orthoclase
Luminescence: None.
Luster: Vitreous (Glassy)
Streak: white
Optical Properties
Optical Data: Biaxial (+), a= , b= , g= , birefringence=0.0130, 2V(Calc)=58, 2V(Meas)= Dispersion none.
Pleochroism (x): colorless.
Pleochroism (y): colorless.
Pleochroism (z): colorless.
From

8. Pyroxenoid:Pyroxferroite
Physical Properties
Cleavage: [110] Perfect, [010] Poor, [001] Poor
Color: colorless, yellow, orange, or pink orange.
Density: , Average = 3.72
Diaphaniety: Transparent to Translucent
Hardness:
Luster: Vitreous (Glassy)
Streak: white
Optical Properties
Optical Data: Biaxial (+), a= , b= , g= , birefringence= , 2V(Calc)=50-58, 2V(Meas)=30-40.
From

9. Pyroxenoid: Pyroxmangite
Physical Properties
Cleavage: [110] Perfect, [110] Perfect
Color: pink, rose pink, purplish pink, yellowish red brown, or brown.
Density: 3.8
Diaphaniety: Transparent to translucent
Hardness: Knife Blade-Orthoclase
Luminescence: Non-fluorescent.
Luster: Vitreous - Pearly
Streak: white
Optical Properties
Optical Data: Biaxial (+), a= , b= , g= , birefringence= , 2V(Calc)=40-42, 2V(Meas)= Dispersion r > v moderate.
From

10. Pyroxenoid: Ferrosilite III
Physical Properties
Cleavage: [210] Good, [100] Parting
Color: colorless, green, dark brown, or nearly black.
Density: , Average = 3.95
Diaphaniety: Translucent to Opaque
Habits: Anhedral Grains - Granular minerals without the expression of crystal shapes
Hardness: Between Apatite and Orthoclase
Luster: Vitreous (Glassy)
Streak: pale brownish gray
Optical Properties
Optical Data: Biaxial (+), a= , b= , g= , birefringence=
Pleochroism (x): pinkish brown.
Pleochroism (z): greenish brown.
From

11. Wollastonite Elasticity

12. Wollastonite Elasticity
From Matsui (1996)