Minerals of Scotland

STRONTIAN

Calcite & Fluorescent Calcite from Strontian.
A Quick Guide to Fluorescent Minerals.

STRONTIAN

Calcite & Fluorescent Calcite from Strontian.
(fluorescent mineral photos courtesy of David Green).

Minerals & Fluorescence - A Quick Guide

Strontian Links

FLUORESCENT MINERALS

Fluorescence in minerals can impress friends and non-mineral orientated people alike.
A small display, or just showing one or two highly fluorescent examples, may astound them!

In the past, fluorescence has been employed in prospecting for scheelite, a tungsten ore,
and the fluorescence of a mineral at a given site may be helpful for identification purposes.

As for rather nondescript specimens - such as those with crystals difficult to distinguish clearly -
these may be transformed, if the mineral has fluorescent properties.

The two photographs below superbly demonstrate this.
In normal lighting, the specimens are not particularly striking but, under ultra-violet light,
they reveal a very clear and dramatic beauty.
(See page bottom for a quick introduction to fluorescent minerals).

CALCITE - Bellsgrove Mine, Strontian, Argyll, Scotland.
(photo courtesy of David Green)

Coroneted CALCITE - Bellsgrove Mine, Strontian, Argyll, Scotland.
(photo courtesy of David Green)

CALCITE from Strontian

Calcite is found in several forms... rhombic, "dog-tooth", discoidal, flos-ferri...
It occurs with all the other species found at the locality.

Though perhaps far from being world-beaters,
they can nonetheless make good specimens.

Crystals may also show a later crystal overgrowth of a differing habit from that of the earlier generation of crystals.

Amongst the latter, are the deep amber, interlocking, rhombic crystal groups found in recent years. Some of these specimens display an interesting internal light play.
The cause of the colouring of these calcites is unknown.

The specimens also fluoresce in Long Wave Ultra-Violet light.

Additionally, amber calcite crystals may also have a partial peppering of tiny harmotome and/or brewsterite micro-crystals on their surface.

CALCITE - Corrantee Mine, Strontian, Argyll.
Sub-parallel, hexagonal prisms with curved pinacoid overgrowing an earlier calcite crystal, 1 cm. in size, of a different habit.

CALCITE from Strontian.
Two examples of calcite's varying and multiple habits:

Left: a scalenohedral crystal to 15mms with a final coating of tiny hexagonal prismatic crystals (see above)
from the Corrantee Mine.
Right: a "coronet" growth on the top of hexagonal prisms
(as seen in the UV calcite photos above)
from the Clashgorm Mine Section.

CALCITE - Strontian, Argyll, SCOTLAND.
(spec- 60x35mms).
Hexagonal crystals to 6mms with a minor peppering of micro pyrite crystals. The form of the calcites almost completely conceals a previous "dog-tooth" habit which has been overgrown (see below).

A secondary overgrowth of hexagonal calcite crystals obscuring an earlier growth phase of the "dog-tooth" habit.
The photos show the varying degrees of the secondary and later overgrowth.

CALCITE - Whitesmith Mine, Strontian.
Scalenohedral crystals to a few millimeters.

CALCITE - Clashgorm Mine, Strontian, Argyll, SCOTLAND.
Rhombic, honey-brown, gemmy crystals to 16mm.
(specimen. c. 110x65mms).

Fluorescence & Minerals

The Ultra Violet spectrum is divided into Long Wave -
the easiest source for the amateur collector to use,
though with the potential drawback that fewer minerals respond to this light source; and Short Wave -
which approaches X-rays in the light spectrum.

The same mineral may fluoresce at one site, but not at another. Some respond to long wave but not short wave and vice versa. Some may respond to both.

A few are always fluorescent - and occasionally with a characteristic colour. Scheelite, is the prime example, responding always in short wave, ultra violet light
with a blue colour. Benitoite is a similar example.

The cause of fluorescence is due either to lattice defects
in the mineral and/ or the result of chemical impurities, which are known as activators.

The high level of fluorescence of fluorite from this classic area, adds an extra cachet other locations do not have.

In Scotland, though not on the same level, but just as interesting, are the examples of fluorescent calcite from Wanlockhead (a rich pink colour in long-wave Ultra Violet light), anglesite from Leadhills, strontianite from the type locality, Strontian (both with yellow tones in Long-Wave) as well as calcite from Strontian.

Studies on Weardale fluorite suggest traces of rare earth elements are an important factor in the fluorescent properties of fluorite from the area.

Elements such as yttrium and europium have been cited (King; Dunham) as well as samarium and gadolinium (Bill/ Sierro & LaCroix).