More

16.4.10: Riesling - Geosciences

16.4.10: Riesling - Geosciences


Riesling beryl
Chemical compositionBe3Al2(SiO3)6Beryllium aluminum silicate
Crystal systemHexagonal
HabitPrismatic
CleavagePoor, basal
FractureConchoidal to uneven
Hardness7.5
Optic natureUniaxial -
Refractive index1.59
Birefringence0.004 - 0.009
DispersionLow, 0.014
Specific gravity2.66 -2.86
LustreVitreous
PleochroismStrong


Riesling beryl was first discovered by a German geologist in 1840 near a small village in East Germany, but unfortunately, the amount they found was small. This link to royalty is one of 4 key components in the pricing this stone.

This stone is actually a pale green color, with a warm golden yellow flash. It is strongly dichroic (green-yellow), which is a second key pricing component as this is unusual in beryl.

It also has a refractive index of 1.59 which is high for precious beryl and is the third key component in pricing. It makes an attractive, sparkly cut stone. (As with all beryl, it is a 7.5 on the Mohs Scale, SG 2.66-2.86)

As there was so little of the material available, it disappeared quickly and was not found again until November 2002, so its rarity is the fourth main pricing component.

At that date, the Everhart family (originally from Germany themselves) found it in Vale of Jequitinhonha near Arcuaii in Brazil. The family was mining for morganite and came across greenish golden stones that were initially thought to be hiddenite. Testing proved them to be beryl.

Still only a small pocket of stones, the rough was exhausted and sent to Italy to sell and exhibit. Remaining rough was sold in the US for cutting and distribution. Some dealers still have material available, but they are very hard to come by. A second pocket, larger than the first Brazilian find, was found in March 2004 but it still produces relatively small amounts of material.

The Jequitinhonha mines produce Riesling beryl as well as pale green and pale golden green. However, it is only the strongly dichroic stones that are considered real Riesling beryl, and it is only these stones that fetch the high prices.

Some collectors recognize only the German material as true Riesling. The only way to be sure from an investment perspective is to obtain a stone with a known provenance. It is difficult but doable. Any good German dealer with a fine reputation will be able to get you one within a week, but the price may be high.

Acknowledgments

  • Martin H. Read
  • Mindat[1]

Watch the video: EXPECTED QuestionsENVIRONMENTAL GeoSCIENCECrash CoursePART23NETSETPhD Entrances