Synthetic vltavins and their differentiation from natural vltavins

Recently, “synthetic wolfavins” have been recorded in places where gemstones and minerals are not commonly traded. Synthetic woolavine is not the correct name for this phase, as a synthetically produced mineral is one that has an identical chemical composition and structure (internal structure) to its natural equivalent. Synthetic wolfavins have, however, minor differences in chemistry and are therefore not true synthetic wolfavins but, rather, imitations of wolfavin. However, for the sake of clarity, we will refer to them as “synthetic wolfavins”.

Crude synthetic woltawines probably first appeared on the market around 2010, first seen at a mineral show in Hong Kong, China. Later on, they could be encountered in other places (Valaderos Governador – Minas Gerais, Brazil, Yen Bai – Vietnam, Hanoi – Vietnam, Ste Maria aux Mines France, Tucson – Arizona, USA, etc.). For the time being, probably all synthetic woltawines have been produced in China.

In 2013, a large number of artificially produced wolfberries appeared at a mineral exhibition in Hong Kong. The quantity was estimated to be around several dozen kilograms. With a surface sculpture that is visually identical to the natural one, these woolavines can be considered a very successful imitation indeed.

Most of the artificially produced vltavins have an unusually high gloss compared to natural vltavins, both from South Bohemia and South Moravia. The only recorded exception was synthetic woolavines found at a gemstone dealer in the town of Yen Bai in northern Vietnam. Natural woolavines have a surface

mostly very sharp (especially the woolly mounds that were dug in sandy sediments), only the woolly mounds that have been transported have a wiped surface, and this wiped surface is

of the abraded visually different. In addition, the sculpture of the wavines that have undergone transport is uniformly replaced by new sculpture obtained by fluvial transport.

“Synthetic woolenware” with an atypical matt lustre – recorded by a merchant in Yen Bai, North China. Vietnam.

“Synthetic woolenware” with an uncharacteristic dull lustre – recorded by a merchant in Yen Bai, North China. Vietnam

Differentiation of “synthetic” and natural vltavins

Almost all of the synthetic woolenware studied so far (438 pieces) have partial edges between the individual protrusions of the sculpture, slightly abraded, with the surface being either significantly shinier (acid-derived shine) or, conversely, significantly duller. The matt surface between

the protrusions could have been formed by etching the cast shape probably with hydrofluoric acid and subsequent very short machining in a vibrating or rolling tambour drum.

The production of sculpture on synthetic vltavins was probably carried out in several ways. The most perfect, i.e. the most similar to true wolfavins, is the clustering produced by selective dissolution with hydrofluoric acid. In a few cases it has been possible to find varnish residues on a few pieces, and also wax residues on some pieces of synthetic wtavins. This material was probably used to cover the surface so that the etching would be as inhomogeneous as possible – selectively, thus producing a very varied sculpture.

Another type of sculpting recorded is the carving of pits and grooves characteristic of woolly marble using a rotating tool, probably a diamond tool, and the subsequent obliteration of the drill marks with hydrofluoric acid. This type of artificial sculpture is relatively easy to detect with a magnifying glass magnifying ten times as much, as the characteristic drill marks remain in the individual pits. In addition, residual residues of hydrofluoric acid etching have been found in the form of a whitish, very thin film in the synthetic wavines produced in this way.

Fluorescent residue after surface retouching with hydrofluoric acid

General view of synthetic woolenware with drilled sculpture

General view of synthetic vltavin with drilled sculpture

Well-smoothed drill marks.

Residual residue after retouching with hydrofluoric acid

General view of the synthetic vltavin with a sculpture made with a drill

Well-smoothed drill marks.

The surface of the pits in the sculpture has a distinctly different sheen from the rest of the sculpture

Close-up view of a dent made by a drill in synthetic vltavin.

Very well retouched drill mark in synthetic vltavin

Lechatelierite inclusions do not sound from protrusions on synthetic vltavine

Close-up view of the drill holes in synthetic wool.

Lechatelierite inclusions do not sound from protrusions on synthetic vltavine

Synthetic vltavine purchased at the mineral show in Ste Maria aux Mines (France).

Synthetic vltavine purchased at the mineral show in Ste Maria aux Mines (France). The shape of this

the stone was, among other things, shaped by a drilling tool and subsequently not perfectly

probably retouched with hydrofluoric acid.

Another type of sculpture is the sculpture created by a cutting tool that was used to make “paths” on the surface of synthetic vltavine and then retouched with hydrofluoric acid. The difference from

to the previous type is that no residual HF etching residue was observed in any case. Compared to the natural sculpture, this sculpture is too perfect; the width of the individual paths is always exactly the same.

General view of synthetic vltavine with too regular sculpture

Too regular sculpture of synthetic vltavine

Lechatelierite inclusions do not sound from protrusions on synthetic vltavine

Natural sculpture on natural vltavín

Too regular sculpture of synthetic vltavine

Too regular sculpture of synthetic vltavine

Natural sculpture on natural vltavín

Another type of artificial sculpture is the sculpture created by casting the enamel into a mould and then finishing the rim on the side with engraving

grinders. This type of synthetic wool is also very easy to identify because of its distinctly unnatural and often perfect appearance.

Synthetic wool in silver, (bought in NY, USA).

Detail of a sculpture on synthetic wool in a ring

Detail of a sculpture on synthetic wool in a ring

In natural waves, especially in the case of whole-forms (dumbbell, disc or drop or larger parts thereof), there is often a significant internal stress. This tension can be easily diagnosed with a polariscope. In crossed nickels, two arms of hyperbolas can be seen approaching each other until they intersect to form a deformed cross. Virtually identical phenomena have been found in synthetic wavines.

But if a shard of wavine is found in nature (including the natural sculpture around the whole piece), then the internal tension has disappeared and the natural wavine behaves completely isotropic in the polariscope (it is still black). Unfortunately, the same is true for smaller pieces of synthetically produced woolavine. This means that the polariscope cannot, probably, be used as a diagnostic test to distinguish between synthetic and natural wool.

Conoscopic image on synthetic vltavine

Conscopic image on the whole shape of natural vltavin

Conscopic image on the whole shape of natural vltavin

In the Chelsea filter, natural wool and its synthetic equivalent have a completely identical reaction (the colour is the same as when viewed without the Chelsea filter). In the UV longwave and shortwave

radiation, natural vltavine is completely inert, whereas synthetic vltavine usually has a faint whitish fluorescence in short-wave UV radiation (254 nm).

Fluorescence of natural (left and middle) and synthetic vltavine (right) in the longwave UV (366 nm)

An important identifying feature of artificial vltavins, especially when mixed among natural vltavins, is fluorescence. Natural tungstates are completely inert at both commonly used wavelengths of ultraviolet light (254 and 366 nm), whereas artificial tungstates have a faint whitish fluorescence at 254 nm.

When determining the density, it is necessary to be very careful that there is no air bubble in the sculpture (both natural and artificially created), because it would float the measured stone and thus introduce a significant error into the whole measurement. Some siltstones, especially from clay sediments, have a naturally “dull” sheen that some customers find less attractive,

Therefore, in the past the surface of these vltavines was greased, mostly with greasy cream, more rarely with oil. It is also very important to wash off this grease from the wool before the actual density determination by the hygroscopic method.

On the other hand, microscopic study is essential to distinguish between synthetic and natural vltavins because all natural vltavins contain lechatelierites and bubbles. All these markers are easily visible with a magnifying glass (10x) or microscope. Other inclusions visible with a conventional gemological or optical microscope are practically absent in vltavins.

Lechatelierite inclusions protruding from the surface of raw natural woltavite

Lechatelierite inclusions in polished natural woltavite

Lechatelierite inclusions in polished natural woltavite

Lechatelierite inclusions protruding from the surface of raw natural woltavite

Lechatelierite inclusions in polished natural woltavite

Lechatelierite inclusions in polished natural woltavite

Lechatelierite inclusions in polished natural woltavite

Lechatelierite inclusions in polished natural woltavite

The typical fluvial structure of the woldavin is very visible in the immersion horizontal microscope, but is often visible macroscopically on polished

vltaviny with the naked eye. Flaxseed oil (n = 1.486) or benzene (n = 1.5) was the best immersion fluid, but it is carcinogenic.

Fluvial structure of natural vltavine

Fluvial structure of natural vltavine

Lechatelierites are quite common inclusions in vltavines, occurring in varying amounts in virtually every vltavine. Lechatelierite is essentially very pure amorphous SiO2. Lechatelierite is not a mineral because it does not have a crystal structure, so it belongs to the mineraloids, but for traditional reasons it is classified as a quartz material.

The lechatelierites are very varied in shape, forming mostly distinctly elongated, often several times axially twisted, foliated formations. More rarely, one can also encounter almost

isometric formations of lechatelierite, the size of which rarely exceeds 1.5 mm.

The lechatelierites always follow the fluvial structure of the volcanic rock. An interesting feature of lechatelierite is also its considerable resistance to chemical alteration, so that numerous cases have been recorded in which lechatelierite has been completely etched out of the fluvium and lechatelierite has been found alone in the surrounding sediment. The lechatelierite is also often only partially etched out of the wtavite, so to speak, “peeking out” from the surface. Cases have also been reported where lechatelierite

form bridges between the two “outgrowths” of the sculptured vltavine. This characteristic of lechatelierite is due to its greater resistance to corrosion than that of wolfavine mass under natural conditions. Knobloch and Urbanec (2003) report that this resistance is about 120 times higher for lechatelierite than for woltavite.

A typical characteristic of lechatelierite is its very low refractive index of light (1.458), for comparison the refractive index of light of woltaulin is 1.48 to 1.54. This difference is relatively easy to observe with an optical microscope using the Becke line method.

Bracelet made of glass imitating wool (bought in NY, USA).

The yellow-green colour of natural wool is due to the presence of low concentrations of Fe

2+

in octahedral coordination (Hanneman 2011). However, this is contradicted by the general assumption that natural glasses are amorphous, i.e. they have only local arrangements at “short range” from a structural point of view, i.e. only tetrahedra

SiO4. In other tektites there is a higher concentration of Fe, which causes their black colour.

One of the ways to safely distinguish vltavine from its imitations is to use Raman spectrometry.

Raman spectrum (170-1500 cm-1

) of natural and synthetic vltavine.

Based on the results from Raman spectrometry, it can be concluded that all measured vltavins have a significant peak around 460 cm

-1. On the contrary

the “synthetic” wolfavin produced in China has two significant peaks around 560 cm

-1 a

1100 cm-1

.

Raman spectrum (0-5500 cm-1

) of natural and synthetic vltavine.

Transmittance spectra of natural vltavine (blue curve), “synthetic” vltavine (red curve) and green Chinese beer bottle (green curve)

Another way to distinguish natural wool from imitation wool quite easily is to measure the UV-VIS absorption spectrum. The picture above shows the marked difference between natural

with fluorine and synthetic fluorine. The natural wtavins have their typical maximum at 580 nm in contrast to the synthetic wtavins which have their distinct maxima at 570 and 740 nm.

Comparison of the properties of natural and synthetic vltavine

Observed property Fluorspar Synthetic fluorspar Chemical composition SiO2 + Al, Ca, Fe, K, Na SiO2 Ca, Na Hardness (Mohs) 5.5 5 Specific gravity 2.35 (2.27-2.46) 2.51-2.53 Fracture None None Fracture Conchoidal Conchoidal Refractive index 1,490 (1,480-1,510) 1,520 Optical Characteristics Isotropic Isotropic Double refraction None None Pleochroism None None Dispersion None None Colour (visual assessment) Light green to

brown-green Lahvovo green

Origin of colour Yellow-green, Fe2+

in octahedral coordination (Hanneman 2011)

Fe2+

Transparency Transparent, translucent Transparent Gloss Glassy to matt Glassy to oily

Fluorescence (UVSW) Inert Faint whitish Fluorescence (UVLW) Inert Inert Fluorescence (X-RAY) Faint yellowish green

(O’Donoghue, 2006) Unknown

Crystal system Amorphous Amorphous Geological origin Impact origin Man-made Inclusions Frequent bubbles, very well

visible fluvial structure, lechatelierite

Infrequent bubbles, usually poorly visible fluvial structure, sometimes flux

UV VIS Absorption spectrum Minimum at 550 nm Maximum at 460 and 640 nm Raman spectrum Maximum 460 cm

-1 Maximum at 560 cm

-1 and 1100 cm

-1.

Conclusion:

Since any destructive analysis cannot be used to distinguish between “synthetic” and natural vltavins, it was necessary to find a simple non-destructive test. Of all the methods tested, finding lechatelierite inclusions either in the intrinsic woltawin (as inclusions) or protruding from the surface appears to be the most advantageous. In many cases, the more experienced observer only needs a magnifying loupe magnified ten times to find an inclusion protruding from the surface. More comfortable, however, is the use of a classical gemological microscope or at least a binocular magnifying glass. If it is impossible to find the lechatelierite inclusions protruding from the surface (they may be completely destroyed by water transport), then it is necessary to find the lechatelierite inclusions directly in the mass of woltavite.

For this, the use of a horizontal gemological microscope and immersion (linseed oil (n = 1.486) or benzene (n = 1.5)) has worked well. For the raw woollens, a combination of different types of illumination (darkfield, daylight, ring LED illumination around the objective) on a gemological microscope has also worked well in finding lechatelierite that protrudes from the surface (mostly from sculpture protrusions). In cut woolly quartz, a mere tenfold magnifying glass is sufficient to find this characteristic inclusion. Among more advanced gemological methods, the use of the absorption spectrometer (UV-VIS) and Raman spectrometry can be recommended. Both methods have sufficiently characteristic spectra.