Examination
of Untreated Tenebrescent Scapolite and comparison with (newly)
irradiated Tenebrescent Scapolite
By Hamid Usman Khattak
(HUK)-Accredited Gemologist
Introduction
Tenebrescence, also known
as reversible photochromism, is the ability of minerals to change colour when
exposed to sunlight. The effect can be repeated for an unlimited or unspecified period of
time, but is destroyed by heating.
Tenebrescent Scapolite was
first found in Badakshan, province ofAfghanistan in 2005. This
unique colorless material is mined near the Hackmanite
deposits and changes an aquamarine colorwhen exposed to LW/SW UV light. This change of color is depending upon the
time it has exposed to Ultra violet light. This change of color is not
permanent it faded gradually almost in 30 seconds (Depending the lighting
condition).
Note:
In tungsten light tenebrescent scapolite faded its color very quickly but in
fluorescent light the change in color is slowly.
 |
| Natural colorless tenebrescent scapolite |
 |
| Natural colorless tenebrescent scapolite |
Aim of
the Experiment: Gems & Gemological Institute of
Pakistan (GGIP)-Peshawar recently
identified a number of tenebrescent scapolite that have undergone
irradiation treatment. The effect of these Tenebrescent scapolite in UV are unusual,
duration of tenebresencent are prolonged and
colored are more intense than Untreated scapolite. During microscopic study deformation and twist in
inclusions are observe.
•Details of the Experiment
•For
this experiment I (HUK) selected 6 cut and polished colorless scapolite. 2 pieces (fig#1) are left behind untreated
and Small 4 pieces (Fig#2) are further chosen for irradiation treatment.
After Irradiation the color of the scapolite is unchanged but 3
type of changes are observe
1.Fluorescence
effect
2.Effect
on Tenebrescent duration and color intensity
3.Inclusions
With the help of these three types of changes,
gemologist and trade people can easily
identify in between the untreated tenebrescent scapolite and irradiated tenebrescent scapolite.
1.Fluorescence
effect
•It
is observed that irradiated scapolite show dull fluoresce effect in LW/SW as compare to
untreated scapolite.
2. Effect on Tenebrescent duration and color
intensity
Untreated tenebrescent scapolite fades its color in
almost 30 seconds
but
It is observed that the scapolite which are irradiated
have tenebrescent property for prolong
period (depend on environment) and color intensity is very dark blue (Kashmir
sapphire color, Fig#6 & Fig#7). At normal room light (energy saver bulbs,
Tube light) it duration is up to for 2 hour to 15 hours (depend on light condition)
and gradually the stone color changes from dark blue to colorless. If the
irradiated stones are placed in diamond parcel or in strongbox or in dark room then
upto 1 month the blue
color exist in the stones(Fig#8). It is also observed that the stone are more
quickly fade in Tungsten
light as compare to
fluorescence light (energy saver bulbs or tube light).
3. Inclusions:
•Inclusions are very helpful in detection of irradiated scapolite. In irradiation scapolite mostly the
inclusions are deform or twist.
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