Canadian Rockhound: Drusy Quartz and Calcite Vug from Graham Island, British Columbia

It all started with a bang one Sunday afternoon as we started hitting a 4-foot boulder of basalt with a sledgehammer. Dale, the cat operator, knew where the good pieces that had rolled off the road might be. The snow was still on parts of the mountain road. He had spotted a large boulder with a small vug the size of your palm. The green drusy covered with white and pink calcite cubes seemed to stretch way back. This was a big boulder! We only had a couple of sledgehammers and no chisels. Luckily, we had an old wooden handled Smarts Canada prospector's pick. As one of us held the handle, the other swung the sledge. It worked great as we followed the cracks on the face. The pick opened them up. After an hour of slugging away, we ran out of steam. Yet, we managed to get the beautiful 16 x 12 inch vug that opened up for us. The photograph below shows the specimen we found.

Quartz and calcite specimen
Specimen with drusy quartz (green) and
calcite (white) crystals.

Closeup
A closeup of the drusy quartz and calcite crystals within the vug. Specs of pyrite were also noticeable on some of the calcite crystals.

The identity of the green drusy that covered the vug eluded us at first. With the help of the Canadian Mineral Society and the Royal Ontario Museum, the identity of the green drusy was quickly determined. We forwarded a specimen to the Royal Ontario Museum in Toronto for analysis. Malcolm Back, who examined the specimen, identified the bladed white crystals and the loose rosette of white crystals as calcite. According to Malcolm, the grayish-green "druse" of tiny colourless crystals was quartz. This made sense, since quartz and calcite can occur in association with each other. The green colouration in the quartz was due to the underlying rock matrix.

The basalt from the locality is from the Tertiary period and is found in the Masset Formation. It overlies the interior of Graham Island. Graham Island is the northern most of the Queen Charlotte Islands, which are situated west of Prince Rupert, B.C. According to the Geology of the Queen Charlotte Islands by Sutherland Brown, the Masset formation is an accumulation of very thick volcanic flows and pyroclastic rocks that are composed mainly of alkali basalt and sodic rhyolite. The basalts may be upper mantle material. Their age is approximately 62 million years or Paleocene.

Acknowledgements:

I sincerely thank Malcolm Back of the Royal Ontario Museum, Mark Mauthner of the Pacific Mineral Museum in Vancouver, and Dirk Schmid of the Canadian Mineral Society for their help in determining the identity of the minerals in the specimen.

References:

Sutherland, Brown. "Geology of the Queen Charlotte Islands, British Columbia"

This article may not be copied, distributed or reprinted in any form without the author's permission. To contact the author, please use the e-mail address provided. If you are unable to contact the author, please contact the Canadian Rockhound. Authorized reprints must acknowledge the author and the Canadian Rockhound.

You may also contact the author using the address below. Please do not send unsolicited mail.

Dutes Dutheil,
Crystal Cabin Gallery Rock and Gem Gift Shop,
7 Richardson Rd.,
Tlell, BC,
Canada, V0T 1Y0.
Tel: (250) 557-4383