THE MINERAL ANDALUSITE

  • Chemistry: Al2 SiO5, Aluminum Silicate
  • Class: Silicates
  • Subclass: Nesosilicates
  • Uses: in the manufacture of spark plugs etc, as a gemstone and as mineral specimens.
  • Specimens
Andalusite is named for its type locality of Andalusia, Spain. It is a polymorph with two other minerals: kyanite and sillimanite. A polymorph is a mineral that shares the same chemistry but a different crystal structure with other minerals.

A unique variety of andalusite is called "chiastolite". It contains black or brown clay and/or carbonaceous material (often graphite) inclusions in the crystal. These inclusions are arranged in regular symmetrical shapes - especially prized when they are in the form of a cross or X.

PHYSICAL CHARACTERISTICS:

  • Color is white, red, brown, orange and green.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is Orthorhombic; 2/m2/m2/m
  • Crystal Habits include prismatic crystals with a square cross section terminated by a pinacoid. also massive and granular.
  • Cleavage is good in two directions.
  • Fracture is splintery to subconchoidal.
  • Hardness is 7.5
  • Specific Gravity is approximately 3.15+ (above average)
  • Streak is white.
  • Associated Minerals are cordierite, biotite, feldspars, quartz, kyanite and sillimanite.
  • Other Characteristics: dark inclusions produce cruciform shapes in the variety chiastolite. Index of refraction is 1.632-1.638.
  • Notable Occurrences include Andalusia, Spain; Austria; California, USA and China.
  • Best Field Indicators are crystal habit, color, inclusions (if present) and hardness.
ANDALUSITE specimens:
(hover for more info)
ANDALUSITE specimen and-1
$ 30.00
Dims: 1.4" x 1.3" x 1.1" (3.6 x 3.3 x 2.8 cm)
Wt: 2.48 oz. (70.3 g)
Malacacheta, Minas Gerais, Brazil
Upon first glance, I thought that this was simply a piece of moonstone, or another related feldspar. This Andalusite specimen does look similar. However, it is definitely Andalusite, as I saw a small piece that had chipped off of another specimen, which had the obvious pleochroism that one expects of this mineral. This particular specimen consists of an irregular chunk of material that shows crystalline tendencies, but lacks a discernable orthorhombic form. It has a reddish-brown coloration and a luster that ranges from waxy to almost vitreous. Though as a whole the specimen is opaque, it does show clarity in several spots that extends a few millimeters into the stone. It is so heavily internally-fractured, however, that one could not hope to see through it. The light that passes through these thin, transparent layers is often reflected back, showing what appears to be a strange iridescence.
no photo
and-1 ($ 30.00)
Malacacheta, Minas Gerais, Brazil
ANDALUSITE specimen and-3
$ 25.00
Dims: 1.2 x 1.2 x 0.5" (3.0 x 3.0 x 1.3 cm)
Wt: 1.0 oz. (28.8 g)
China
This small specimen consists of a crystal of Chiastolite, a variety of Andalusite. The specimen is actually a cut cross-section of the crystal, and is polished on both of its basal faces. This allows one to see the cruciform design that is likely caused by inclusion of a carbonaceous or clay-like substance during the crystal's formation. Its color ranges from black to brown to a deep cream, and it shows some dim transparence and translucence in a few areas, but is opaque in others. There appear to be fibrous inclusions that are aligned in a radial pattern- I do not know if they are needles that are trapped within, or if they are simply a result of the crystal's formation.
no photo
and-3 ($ 25.00)
China
ANDALUSITE specimen and-4
$ 32.00
Dims: 1.5 x 1.0 x 1.0" (3.8 x 2.5 x 2.5 cm)
Wt: 1.35 oz. (38.4 g)
Malacacheta, Minas Gerais, Brazil
TTwo small, partly intergrown Andalusite crystals make up this thumbnail specimen. The larger of them has dimensions of 1.4 x 0.8 x 0.8" (3.6 x 2.0 x 2.0 cm), and the smaller has dimensions of 0.8 x 0.5 x 0.5" (2.0 x 1.3 x 1.3 cm). Both are in fair condition, as each does show some damage. However, they appear to be more damaged upon first glance than they actually are, due to uneven crystal faces and edges. Thus, their orthorhombic prismatic form is discernable, but not very good. They have a red-brown coloration and a dull waxy luster, and are translucent only around their edges due to extreme internal fracturing. These fractures, however, help to reveal an interesting optical effect- small portions of the material show a milky, glowing schiller akin to that of "moonstone". The crystals likely were surrounded by either crystalline muscovite or a mica schist, as most of their crevices are filled with such material- this is likely the cause of their lack of very good crystal form. There is no other host rock, however.
no photo
and-4 ($ 32.00)
Malacacheta, Minas Gerais, Brazil
ANDALUSITE specimen and-5
$ 25.00
Dims: 1.1 x 1.1 x 0.3" (2.8 x 2.8 x 0.8 cm)
Wt: 16.7 g
near Bimbowrie, Australia
This thumbnail specimen consists of a partly-cut section of an Andalusite crystal. Though it has not been ground or polished, one can definitely see the "cross" effect on its two faces. Other than the dark crust on its side faces and the black veins that form the "cross", it has a pale brownish-green coloration and a dull luster, and is completely opaque in normal light. There is evidence of some sort of mica on its side faces, but no host or base rock is present.
no photo
and-5 ($ 25.00)
near Bimbowrie, Australia
ANDALUSITE specimen and-6
$ 30.00
Dims: 2.2 x 1.7 x 0.4" (5.6 x 4.3 x 1.0 cm)
Wt: 1.92 oz. (54.4 g)
Minas Gerais, Brazil
One of the largest sections of a Chiastolite crystal that I have seen comprises this specimen. Like most pieces of this sort, this section has been ground and polished on both of its "basal" faces to a high gloss. This enables one to see the "cross" that is a hallmark of the species, which divides the section into four quadrants. These quadrants have a moderate brown color with a strong pinkish tinge and are dimly translucent to dimly transparent in clarity. The "cross" itself is black in color. The edgeward faces are somewhat rough and uneven, but show no fresh damage, and there is no host rock present.
no photo
and-6 ($ 30.00)
Minas Gerais, Brazil
ANDALUSITE specimen and-7
$ 27.00
Dims: 1.5 x 1.4 x 0.4" (3.8 x 3.6 x 1.0 cm)
Wt: 28.1 g
Minas Gerais, Brazil
This specimen consists of a polished section of an Andalusite crystal. It is of the variety known as Chiastolite, which is characterized by a dark lines that intersect the crystal at 90-degree angles, creating a "cross". The piece is in very good condition, as only a small amount of damage is visible, and what crystal form it has is reasonably good. The two "basal" faces of the piece have been ground smooth and polished to show off the cross and the resulting quadrants of material that have a pale brown coloration with a pinkish tinge. It is nearly opaque at its center, but the edges of each quadrant are translucent and even dimly transparent to a degree. There is no host rock present, of course.
no photo
and-7 ($ 27.00)
Minas Gerais, Brazil
ANDALUSITE specimen and-8
$ 26.00
Dims: 1.5 x 1.2 x 0.4" (3.8 x 3.0 x 1.0 cm)
Wt: 25.9 g
Minas Gerais, Brazil
This small specimen consists of a partly-cut and -polished slab of Chiastolite, a variety of Andalusite. It has a rounded, warped oblong shape and shows the "quadrants" that are the primary characteristic of this type of Andalusite. Its color is brown with a hint of pink, and the intersecting lines that extend through it are black. The cut surfaces are polished to a high sheen, but the edgeward surfaces have a dull waxy luster. There is no host rock present.
no photo
and-8 ($ 26.00)
Minas Gerais, Brazil
ANDALUSITE specimen and-9
$ 55.00
dims mm=61.30x47.60x35.61
wt g=169.4
Xisha Mine, Hunan, China
This is a highly weathered specimen of andalusite, which has been cut and polished on one cross section to reveal the characteristic cross-shaped inclusions for the variety chiastolite.
no photo
and-9 ($ 55.00)
Xisha Mine, Hunan, China
 

Copyright ©1995-2023 by Amethyst Galleries, Inc.