Geological Specimens
By G. M. Richards, Columbia University1—Pegmatite-Grand Lake. The specimen was taken from a pegmatite dike at its contact with an amphibolite. In the hand specimen it is an apparently pure orthoclase but in the thin section small scattered quartz grains are observed; as well as the alteration products, Kaolin and sericite.
The minerals at contact are quartz, biotite, magnetite and hornblende.
Both the quartz and orthoclase contain dust inclusions and crystallites, while the evidences of shearing and crushing are abundant.
2-Quartz Biotite Schist.
Contact between above dike and amphibolite. A coarse black rock carrying magnetite and pyrites in considerable quantities.
Under the microscope some of the biotite has a green coloration from decomposition and is surrounded by strong pleochroic halos.
Small grains of secondary pyroxene are numerous.
3-Grand Lake.
A dark, compact rock, having a mottled appearance due to grains of plagioclase, and a green color in section.
Minerals present are hornblende, biotite, plagioclase, pyroxene, quartz and the alteration products from the feldspar.
The rock has been subjected to a strong crushing action, which has been resisted by only small portions of it. The spaces between the grains, which are intact, are filled with a confused mass of peripherally granulated minerals, in which strain shadows are very prominent.
The rock has been derived by dynamic metamorphism from a basic igneous rock.
4-Biotite Granite Gneiss.
Eighteen miles above mouth of Nascaupee River. A fine-grained rock of gneissic structure having a faint pink color.
Plagioclase, microcline and quartz are the predominating minerals, while biotite, titanite, epidote, apatite, zircon and garnet are present in smaller quantities.
There is also a small amount of hematite, pyroxene and sericite.
The rock, which is of a granitic composition, contains numerous crystallites and has been subjected to considerable strain and crushing, which has resulted in foliation.
5-Mica Granite Gneiss—Country Rock—near Caribou Ridge.
In the hand specimen the rock has the same appearance as No. 4, if anything, it is somewhat more compact.
The principal minerals are, plagioclase, biotite and microcline, with smaller quantities of quartz, iron oxide, pyroxene and garnet.
The feldspar is decomposed with the resulting formation of epidote, which is quite prominent. There are also numerous included crystals.
The rock has been greatly crushed and sheared, and is much finer than No. 4.
6—Cap of Caribou Ridge.
A hard compact rock of dark green color, having a mottled appearance, due to the presence of a white mineral.
Pyroxene, quartz and augite form the groundmass, as seen in section. There are a few small grains of magnetite.
The severe crushing to which the rock has been subjected has resulted in the conversion of the plagioclase into scapolite and also in the formation of zoisite by the characteristic alteration of the lime bearing silicate of the feldspar in conjunction with other constituents of the rock.
The light mineral is finely granulated and the whole is marked by uneven extinction.
The rock has probably been derived by dynamic metamorphism, from a coarse igneous rock like a gabbro.
7—Epidotic Sericitic Schist. Washkagama Lake.
A fine grained compact gray rock, of aggregate structure, consisting chiefly of quartz, plagioclase and biotite, and the alteration products epidote and sericite.
Under the microscope it is a confused mass of finely granulated minerals, with numerous included crystals.
The rock has undergone complete metamorphism and its origin is unknown.
8—Phyllite-Near Otter Lake.
A soft extremely fine grained gray rock, with a well developed schistose structure, carrying much magnetite, plagioclase, orthoclase and their alteration products.
The strain to which the rock has been subjected has resulted in a very fine lamination, and it isconsiderably weathered.
9—Calcarous Sericite Schist.—Seven Miles East of Seal Lake.
A dark compact rock, in which calcite and sericite predominate. Quartz is less plentiful. The results of shearing and pressure are very prominent and bring out the foliation, even in the calcite.
10—Schistose Limestone—Same location as No. 9.
A white rock having a peculiar mottled appearance due to the inclusions of decomposing biotite which project from the surrounding mass of calcite. There is some sericite present, also magnetite, resulting from the decomposition of the biotite.
The bent and metamorphosed condition of the calcite shows the shearing and crushing which the rock has undergone.
11—Phyllite—same location as No. 9.
A dark red, finely laminated rock consisting chiefly of decomposed biotite and feldspar, occasional quartz grains and sericite and much iron oxide.
The rock has been subjected to strong shearing force, producing a good example of schistose structure.
12—Quartzite—Same location as No. 9.
A compact rock of light red color, made up of uniformly rounded grains of quartz, and the feldspar with occasional grain of magnetite.
A fine siliceous material discolored by iron oxide, acts as a cement between the grains.
The quartz grains show secondary growth. 13—Altered Gabbro—Thirty-two Miles Above Wuchusk Nipi on Nascaupee River.
A coarse dark green rock whose principal constituents are pyroxene plagioclase and magnetite.
There is a slightly developed diabasic structure and the rock is much altered by weathering; the resultant product being chlorite.
14—Quartizite—Bibiquagin Lake.
Hard compact rock of light red color, cut in all directions by narrow veins of quartz, from microscope size to one-half an inch in width.
The grains of the constituent minerals, quartz, feldspar and magnetite have an angular brecciated appearance; showing uneven extinction and strong crushing effects.
The magnetite is somewhat decomposed, the resulting hematite filling the spaces between the quartz grains.
15—Anorthosite—Shore of Lake Michikamau.
A coarse grained rock of dark gray color, in which labradorite is the chief mineral. Magnetite and Kaolin are present in small quantities.
The labradorite contains inclusions of rutile and biotite and has a well-developed wedge structure and cross fracture due to the pressure and shearing which it has undergone.
It is also somewhat stained by the decomposition of the magnetite.
On the map of the portage route to Lake Michikamau; that lake, the Grand River and Groswater Bay are taken from the map accompanying the report of Mr. A. P. Low.
The location of the Susan and Beaver Rivers with their tributaries was obtained from Dillon Wallace’s map in “The Lure of the Labrador Wild.”
The instruments used were a Brunton Pocket Transit, a small taffrail log and an Aneroid Barometer. Distances on land were approximated by means of a pedometer and by rough triangulation.
Map of Canoe Route from Lake Michikamau to Ungava Bay and Sledge Route from Fort Chimo to Nachvak Bay
Map of Portage Route from Hamilton Inlet to Lake Michikamau Labrador