THE MINERAL BUERGERITE (A Tourmaline)

  • Chemistry: NaFe3Al6Si6O18(BO3)3O3F, Sodium Iron Aluminum Boro-silicate Oxide Fluoride.
  • Class: Silicates
  • Subclass: Cyclosilicates
  • Group: Tourmalines
  • Uses: Only as mineral collection specimens
  • Specimens
Buergerite is a rare species of the Tourmaline Group. Other more common and at least more well known tourmalines are schorl (black, opaque and iron rich), uvite and the gemstone mineral, elbaite (various colors, transparent to translucent and lithium rich). Buergerite is usually easy to distinguish from the more common tourmalines. It is generally brown and translucent to opaque. Buergerite is more easily confused with the lesser known tourmaline, dravite. It is very difficult to distinguish dravite from buergerite under normal circumstances since both are brown and only slightly translucent. However dravite is formed in metamorphic rocks and buergerite is found in some very unusual extrusive igneous rocks (volcanic rocks).

Buergerite, when first discovered, was considered to be an unusual variety of schorl, another sodium iron tourmaline. But, the iron in buergerite is different than in schorl. In schorl, the iron is in the plus two (+2) oxidation state, but in buergerite the iron is in a plus three (+3) oxidation state. This makes buergerite a rather unusual tourmaline. To compensate for the extra +3 charges (one extra charge from each of the three iron ions in the formula) buergerite must substitute three of the four hydroxides (with a -1 charge each) , that are normally present in a typical tourmaline, for three oxygens (each with a -2 charge) in order to balance the formula. In addition to this odd-ball setup, buergerite has a fluorine (with a -1 charge) instead of that last hydroxide. Despite all of this chemical mayhem, buergerite still retains its tourmaline structure and most of the typical tourmaline characteristics.

PHYSICAL CHARACTERISTICS:

  • Color is dark brown.
  • Luster is vitreous.
  • Transparency: Crystals are translucent to opaque.
  • Crystal System is Trigonal; 3 m
  • Crystal Habit is typically elongated three sided prisms. The terminations can be either a simple to complex trigonal pyramid or a flat basal face. The prism faces are striated lengthwise. In cross section, all tourmalines will appear predominantly triangular in shape with some crystals showing a hexagon. Doubly terminated crystals are hemimorphic meaning that the two ends of the crystal are not exactly alike. Massive specimens can also be found.
  • Cleavage is absent although there is basal parting.
  • Fracture is uneven to conchoidal.
  • Hardness is 7 - 7.5
  • Specific Gravity is 3.3+ (slightly heavier than average)
  • Streak: Off white.
  • Other Characteristics: Pleochroic and piezoelectric.
  • Associated Minerals include those commonly found in volcanic rocks.
  • Notable Occurrences is mostly limited to San Luis Potasi, Mexico.
  • Best Field Indicators are crystal habit, triangular cross-section, locality, environment, color and hardness.
BUERGERITE specimens:
(hover for more info)
BUERGERITE specimen bue-4
$ 48.00
Dims: 0.83x0.78x0.57" (2.10x1.98x1.45cm)
Wt: 0.22oz (6.3g)
Mexquitic, San Luis Potosi, Mexico
Perched on one corner of this host rock are several crystals of buergerite. They are brown and opaque, except for golden highlights that reflect from a bright light. The crystals (while small) are large enough to see the hexagonal structure and lengthwise striations typical of tourmalines (a family in which buegerite belongs). A loupe reveals excellent crystals with golden highlights reflecting from internal fractures, making this prettier than any dravite specimen that I have seen. The largest crystal measures 4 or 5 mm long.
no photo
bue-4 ($ 48.00)
Mexquitic, San Luis Potosi, Mexico
BUERGERITE specimen bue-1
$ 45.00
Dims: 0.30x0.29x0.23" (0.77x0.74x0.58cm)
Wt: 2.5ct (0.5g)
Mesquitic, San Luis, Potosi, Mexico
This is an excellent example of the rare tourmaline, buergerite. It has the typical luster and form of tourmalines, and to my eye the brown color is different than that of dravite. The crystal is nearly opaque - the only hints of translucency comes from the surface texture, which does look translucent to transparent at a barely perceptible level under a 15x loupe. The specimen is nearly doubly terminated and undamaged, except for a missing section near the top where a cavity exposes what I think is the remainder of another buergerite crystal that broke away. There are also a number of prismatic cavities which once held quartz crystals - a few of which remain on the specimen. The back side of the crystal is incomplete, and a loupe shows that it consists of several partial crystals and is likely the attachment point to the original substrate.
no photo
bue-1 ($ 45.00)
Mesquitic, San Luis, Potosi, Mexico
BUERGERITE specimen bue-2
$ 35.00
Dims: 0.41x0.33x0.26" (1.03x0.83x0.66cm)
Wt: 0.03oz (0.8g)
Mesquitic, San Luis Potosi, Mexico
This is a cluster of crystals of the "other" brown tourmaline, buergerite. While it is considered difficult to distinquish from dravite, this specimen looks quite different than most dravites. It has a pattern of gold highlights that give it an interesting surface luster, very nice. Also, several of the crystals are excellent (although all are small), having good form and even being doubly terminated.
no photo
bue-2 ($ 35.00)
Mesquitic, San Luis Potosi, Mexico
BUERGERITE specimen bue-3
$ 35.00
dims mm=8.86x7.98x6.05
wt g=0.6
Mesquitic, San Luis Potosi, Mexico
This is an excellent crystal of buergerite, a brown tourmaline. It has a very appealing surface luster when viewed with a loupe.
no photo
bue-3 ($ 35.00)
Mesquitic, San Luis Potosi, Mexico
 

Copyright ©1995-2023 by Amethyst Galleries, Inc.