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THE PACIFIC MINERALOGIST 13

WHITE MAGIC WITH BLACK LIGHT
By THOMAS S. WARREN
The commercial applicatio,n of ultra-vio,let light to minning, while only about five years
old, has a numbe1r o,f no,teworth,y successes to its credit. It ha,s proved to be of particular
value in the prospecting for scheelite because scheelite is the most impo,rtant commercial
mineral which fluo,resces.
Imagine operating a gold mine for ue and others are practically useless.
50 years and then to find that there In the first place, ordinary light will
was enough scheelite in the tailings not create fluorescence. Flourescence
to have paid the operating expenses is the result of a stimulation to the
of the mine! atoms of the mineral. There are
Imagine, too, the disappointment two general groups of ultra-violet
of the lone prospector in Arizoncr wa ve lengths - the long wave
who had dug a tunnel for 50 feet lengths and the short wave lengths.
along a vein (always hoping that the The long wave length ultra-violet will
gold values would increase and that stimulate fluorescence in a few ma-
his prospect some day would be- terials, such as dakelite, semi-opal,
come a mine) when he learned that wernerite, benitoite, and fluorite. On
he had thrown a fortune in scheelite the other hand, the short ultra-violet
on the dump. wave lengths will cause fluorescence
Or again, imagine the prospector of over 300 minerals, including all
on a California desert who dug six the minerals listed above that fluor··
prospect holes in the side of a moun- esce by means of the long wave
tain, three of which uncovered an lengths. Among these many miner-
extensive deposit of scheelite, but als are barites, calcites, colernanite,
abandoned the holes as there was hackmanite, halite, hydrozincite,
not enough lead in the property to kunsite, opal, pectolite, scheelite,
warrant further assessment work. wollastonite, and smithsonite.
Yet the next man was in line for While there are a number of ultra-
a fortune, because he used a fluor- violet light sources, there is only one
escent lamp and discovered the source of the short wave lengths
scheelite which had been discarded; and that is a genuine quartz light
There are innumerable such cases equipped with a special filter which
which might be used to illustrate the screens out the visible light and
value of an ultra-violet black light allows the transmission of only the
for mining purposes. Scheelite is ultra-violet. None of the other ultra-
used here as the example because violet light sources transmits the
scheelite is the most common fluor- short wave lengths, and for this rea-
escent commercial mineral, but there son their use is very limited in the
~-
are hundreds of other uses for the mineral field. The only type of light
Mineralight black lamp. which can be used in prospecting
Night prospecting is an unusual for scheelite is the coiled quartz tube
but a very profitable development of lamp.
rece~t years. The old-time pros- Many prospectors have attempted
pector considered his work done to make their own black light lamp
when the sun had set, but many by using a filter in front of an ordi-
modern prospectors are just begin- nary flashlight bulb. This filter
ning their work when .the sun goes screens out the visible light, but there
down. The instrument which has are none of the short ultra-violet rays
changed this procedure is the ultra- formed by the bulb. As a result, the
violet black light. lamp is useless in the detection of
It might be best at this point to ex- scheelite. These long wave ultra-
plain why certain lamps are of val- violet rays do not cause the fluor-