by Ronald Werner
After a number of not so very succesfull rocktrips til remote localities, me and a collecter friend decided to visit the rock quarry at the other side of the Heddal Lake. In a straight line from where I live, the distance couldn't be much more than 2 kilometers. From my kitchen window I can see those abandoned quarries....
Why these quarries never seemed to be able tempt us before, I don't know. Maybe it has to do with the saying, that all good things come from afar. Anyway, we found out that the grass being greener at the other side, doesn't mean one has to travel to the other side of Norway. The other side of Heddal Lake turned out to be far enough!
Tinfos Jernverks Kvartsbrudd is a quartzite quarry, where relatively pure quartz was taken out for the production of ferro-silicium in the smelter in Notodden, the Tinfos Jernverk. The Tinfos Jernverk was closed down about 10 years ago, and simultaneously the quarries were abandoned.
The quarry made a very virginal impression on us, with no or hardly any signs of collecters having cleaned the place for minerals, and leaving a pile of trash behind. (This, probably, as a fair exchange between nature and mankind..?!)
Anyway, if there had been collecters in the quarry, they certainly didn't collect micro-minerals. For in less then half an hour we collected a nice pile of material containing some of the finest micro turquoise I have ever seen.
The quartzite in the quarries is obviously layered and full with fractures. Narrow open veins occur throughout the quarry, but are rarer. The fractures show at many places signs of iron mineralisation, but copper mineralisation is limited to one single small area in the south quarry.
Brastad describes as early as in 1980 pseudomalachite and turquoise as fine-grained mineral in the fractures in the quartzite. This material was found as loose boulders, and no mineralisation was found in wallrock.
We found both the turquoise and pseudomalachite in loose boulders, obviously material blasted out just before the qyurry was abandoned. But we could also see the pseudomalachite and turquoise in the wall in a zone of 2-3 meters wide.
The explanation for the copper mineralisation is uncertain. My personal theory is that a metamorphosed diabase/gabbro-dike in the southern part of the quarry might have been the source for copper-containing solutions.
ANATASE was found in only a few samples. The crystals were nice yellow-brown, bi-pyramidal and have a size of up to 1 mm. The anatase was found in association with hematite.
CHLORITE is common as typical green micaceous or worm-like aggragates. Often altered to limonite.
GOETHITE is found as limonite and very rarely as brown, radiating crusts, or as balls
HEMATITE is very common as brown powderish/fine-grained filling of fractures. Somewhat less common as nice, black metallic, tabular crystals up to 2-3 mm. Also in epitaxial growth with rutile.
PSEUDOMALACHITE can be found as emerald green stain in the fractures. Crystals or esthetic specimens have not been found. Neuman ('86) describes the find of pseudomalachite by Jamtveit in 1980.
QUARTZ is omni-present in the veins as small, clear crystals up to a couple of millimeters. In some larger cavities crystals up to several centimeters have been found, according to some locals we spoke. These are white, translucent and supposedly not too nice. The remains we found were not of any interest to us.
RUTILE can be found as tiny sagenite aggregates and in epitaxical growth with hematite. These resemble more or less the epitaxies of Vinstra in a much more modest form. The brown hair-like crystals are never more than some tenths of a millimeter long.
TURQUOISE is by far the most interesting mineral from the Tinfos Jernverks Kvartsbrudd. Most of the turquoise is massive and of no interest to collecters. But not uncommonly in loose material, it is possible to find beautifully crystallized turquoise in cavities.
Most of the turquoise can be found as nice blue globular aggregates of distorted pseudo-rhombohedral crystals (pict. 1 & 2). Sometimes it is possible to actually recognize pseudo- rhombohedral crystals (pict. 3, 4 & 5). Very rare are the sharp-pointed, tabular rhombohedral crystals shown at picture 6. The crystals are transparant to translucent, and usually less than 0,1 mm in size. The globular aggregates can be up to 1.5 mm in a single case.
Jamtveit (Neumann 1986) found in his time no turquoise in the wallrock, but we could observe massive blue turquoise in fractures in the wall. We found no cavities with crystallized turquoise in this zone. Only the blasted out material contained crystallized turquoise.
TOURMALINE was found in only one large boulder, but there was plenty of it. The black, short to long prismatic crystals are dark red-brown translucent under the microscope. My guess is that it must be either schörl or dravite. The crystals are found embedded in the quartzite and can be up to almost 1 cm with a thickness of about 1 mm.
Additionally we found a mica-like mineral as subordinate rock-forming mineral in the quartzite, which probably will be muscovite. A white massive, kaolinite-like mineral is found in some of the cavities.
This quarry has hardly been visited by collecters and should still yield the patient collecter a number of nice turquoise samples. Access to the quarry is unproblematic, as long as you behave yourself.