ART. XXXVII.-Contributions to the History of Euphotide and Saussurite; by T. STERRY HUNT, of the Geological Survey of Canada.

1. The name of euphotide was originally given by Haiy to a rock composed of diallage and a white compact mineral which he designated as feldspath tenace, (the compact feldspar of Werner, the lemanite of Delamétherie, and the jade of de Saussure senior). The well-marked contrast of colors which suggested the name of euphotide is seen in the beautiful verde di Corsica or verde antico di Orezza, and in some varieties of the rock from Mt. Rose. In these the diallage is represented by a grass-green smaragdite, and this mineral and hypersthene being regarded by Hauy as varieties of diallage, he included under the head of euphotide, the verde di Corsica, (for which alone d'Halloy retains the name of euphotide,) the hypersthenite or hyperite of other authors, and the granitone of the Italians. This last by an error of Von Buch, in which he has been followed by Gustav Rose, is very frequently called gabbro. The true gabbro of the Italians is however a diallagic ophiolite. (Brongniart, Classif des Roches, 1827, p. 75.)

Brongniart defines euphotide to be a mixture of diallage with jade, petrosilex, or compact feldspar, and including d'Halloy's two species, euphotide and granitone, but excluding hyperite, he distinguishes as varieties, jadian and feldspathic euphotides, besides ophitic (serpentinous) and micaceous euphotides, the latter being sometimes talcose.

Coquand (Traité des Roches, 1857,) has followed Hauy with regard to the euphotides, while Senft (Die Felsarten, 1857,) places in one group, under the head of hyperite, three genera, eclogite, gabbro, and hypersthenite, in the second of which he includes rocks made up of labradorite or saussurite with diallage or smaragdite. The eclogite of Hauy is composed of diallage or smaragdite, and red garnet; it often holds disthene (cyanite) through the predominance of which it passes into disthenite (disthenfels), while hypersthenite or hyperite (hypersthenfels, G. Rose) is a mixture of saussurite or labradorite with hypersthene (d'Halloy, Senft.).

Distinctions like some of the above based upon the contained varieties of pyroxene are evidently of secondary importance, and it becomes necessary to define with more strictness the nature of the other element of the rocks in question. The jade of the Swiss Alps to which de Saussure junior, afterwards gave the name of saussurite, was described by de Saussure senior, as compact, tenacious, greenish-white in color, hard enough to scratch quartz, and having a specific gravity of 3·318—3·389.

Mohs gives 3.256 for the density of a granular saussurite from Peidmont, and 3.34 for a compact variety from the Canton of Vaud, while Naumann assigns to the mineral a density of 3.40. These authors thus agree in ascribing to saussurite a specific gravity much above that of the feldspars.

Klaproth and de Saussure junior, both analyzed specimens of the saussurite from the shores of the Lake of Geneva (lemanite, I and II) while Boulanger subsequently examined the saussurite from the euphotide of Mt. Genèvre (III), and from two localities in Corsica, the valley of Orezza (IV) and the banks of the Fiumalto (V).

Silica,

I.

II.

III.

IV.

V.

The physical and chemical characters of the above specimens offered considerable differences. The saussurite II. is described by de Saussure as leek-green, subtranslucent, with an oily lustre, and a finely granular, scaly fracture; it scratched quartz and had a density of 3.261. At a high temperature it fused without loss of weight, into a glass much softer than the original mineral, and having a density of only 2.8. This saussurite, which was free from any admixture of smaragdite, was scarcely attacked by boiling sulphuric acid. (Journal des Mines, vol. xix, p. 205, A. D. 1805.)

The saussurite from Mt. Genèvre (III) according to Boulanger is associated with a greenish-brown smaragdite, and is itself greenish-white and compact, not scratched by the knife, and having a density of 2-65. He describes another euphotide from the same locality as having a lamellar base, with cleavages like feldspar, sometimes chatoyant, hard, not attacked by acids, and with a density of 2:58. The analysis of this undoubted feldspar gave him, silica 66·6, alumina 18.5, lime 1·8, soda 6·0, potash 43 97.2.

=

The euphotide of Orezza is described by Boulanger as composed of green diallage, a blackish matter also apparently a variety of diallage, and saussurite, the whole arranged in parallel bands, giving to the mass, which is very tough, a schistose fracThe saussurite (IV) was very compact, less hard than III, and had a density of 3 18. It was easily fusible and not attacked by concentrated sulphuric acid.

ture.

* Besides 0.05 oxyd of manganese.

SECOND SERIES, VOL. XXVII, No. 81.-MAY, 1859.

The euphotide of the Fiumalto consisted of green diallage with curved lamella in a white paste, which was tender, easily cut with a knife, and had a density of 330 (v). It was readily fusible and easily attacked by sulphuric acid, with which the analysis was made; the separated silica being dissolved by a solution of potash which left a residue, supposed to be diallage, and equal to 3-8 parts, which added to the above analysis makes the sum 100-4; alkalies were absent.-(Ann. des Mines, [3], viii, p. 159.)

Notwithstanding the peculiarities presented by saussurite, modern mineralogists have generally referred it to labradorite or some other feldspar, (see Beudant, Bischoff, Dana, Delesse, etc.). Jameson, separates it from the feldspars on account of its greater specific gravity, but recent authors seem to have entirely lost sight of this characteristic. Coquand describes saussurite as having a density of 2.87, while according to Delesse it is seldom inferior to 2.80. These authors agree in declaring the mineral to be decomposable by acids like labradorite, while Bischoff and Senft, without alluding to its density, assert that saussurite is not attacked by acids.

An analysis of saussurite by Stromeyer gives the composition of labradorite, while Lory on the other hand has described as euphotide a rock from Levaldens in the Dauphinese Alps, which is made up of an olive hornblende and a white mineral having the cleavage of a feldspar and the composition of andesine. -(Bull. Soc. Geol. de France, [2], vii, 540.)

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Delesse examined the white base of a euphotide from Odern in the Vosges, and another from Mt. Genèvre. Both of these were highly crystalline and exhibited the polysynthetic macles of the feldspars of the triclinic system. When pulverized and treated with muriatic and sulphuric acids they swelled up and were decomposed. Delesse has however described them as saussurite. That from Odern gave him, silica 55.23, alumina 24-24, lime 6.86, magnesia 1-48, protoxyd of iron 111, soda 4.83, potash 303, water and volatile matters 3:05 99.83. The euphotide of Mt. Genèvre contained diallage, a serpentine-like substance, and a ferriferous carbonate of lime, besides the feldspar, whose crystalline lamina were more than one-third of an inch in length, and gave by analysis, silica 49-73, alumina 29.65, lime 11.18, magnesia 0-56, protoxyd of iron 0.85, soda 4.04, potash 0-24, water and volatile matters 3.75 100.00. Of the volatile portion according to Delesse, at least 2.50 p. c. is water, the remainder being carbonic acid. (Ann. des Mines, [4], xvi, pp. 238 and 267.) This feldspar resembles that of the orbicular diorite of Corsica which gave to Delesse, silica 48-62, lime 12.02, alkalies 3.61, and 0.49 of water.

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Under the name of saussurite von Rath has described a mineral which with hornblende (uralite) forms the greenstone of Neurode in Silesia. It had the hardness, cleavage, and crystalline structure of labradorite, but with a specific gravity of 2.99, and gave by analysis, silica 50-84, alumina 26.00, peroxyd of .iron 2.73, lime 14.95, magnesia 0.22, potash 0.61, soda 4.68, volatile 1.21 101.24.-(Pogg. Ann., xcv, 555.)

2. Accepting the view maintained by Rose, Bischoff and Delesse, that saussurite is nothing more than a feldspar, I referred to this species the compact feldspars of the Laurentian rocks of Canada, described in my report of 1854. Associated with the limestones and ophiolites of this most ancient geological series, is a great body of crystalline stratified rocks, composed essentially of anorthic feldspars, sometimes almost without admixture, but frequently associated with green granular or cleavable pyroxene, which passes through passes through a kind of bronzite into hypersthene. Small quantities of epidote, garnet, and more rarely mica and quartz, are also met with, and magnetite and ilmenite are common. Different varieties of these rocks would be referred by lithologists to the species labradophyre, dolerite, and euphotide. The feldspars are sometimes very coarsely crystalline but often compact; they have a hardness of 6.0, and vary in density from 2.67 to 2.73, and in composition from andesine to vosgite. The denser varieties are those in which lime and alumina predominate; all of them contain besides soda small quantities of potash. The analyses of numerous varieties of these feldspars will be found in the Report cited above, and in the L. E. and D. Philos. Magazine, [4], ix, 262.

The euphotides examined by Delesse and Lory are apparently nothing more than varieties of dolerite, by which term we understand a rock composed essentially of a triclinic feldspar, with some variety of pyroxene, which may be augite, hypersthene, or diallage. According to G. Rose, smaragdite, which is the variety of pyroxene regarded as characteristic of euphotide, has often the external form of pyroxene with the cleavage of hornblende, constituting the variety uralite, while in the euphotides of Baste and Veltlin hornblende occurs with the diallage, and sometimes replaces it entirely, giving rise to a rock composed of saussurite and hornblende. Sandberger has observed crystals of pyroxene forming macles with others of hornblende, and the latter often surround the crystals of pyroxene, or as I have remarked in specimens from Madawaska, small crystals of deep green hornblende are implanted upon large prisms of greenishwhite pyroxene. Smaragdite according to Hisinger and Delafosse consists of laminæ of pyroxene and hornblende united in a more or less regular manner. Since diorite is distinguished from dolerite by the substitution of hornblende for pyroxene, it

is evident that feldspathic aggregates like those of Baste present a transition from the one to the other species of rock.

Diorite is distinguished from diabase according to Senft by containing a feldspar insoluble in acids (albite or oligoclase,) and by the frequent presence of quartz, while in diabase the feldspathic element is less silicious and decomposable by acids; (labradorite or a variety approaching anorthite).* When however we consider the manner in which these feldspars pass into one another, this distinction between diorite and diabase seems of but secondary importance. We have seen that the orbicular diorite (or diabase) of Corsica contains a feldspar near anorthite in composition, while others in the Vosges, according to Delesse, contain labradorite and andesine, the latter with quartz. Lory has described a diorite from the crystalline schists of the mountains of Chalanches (Isère) which is made up of a chromiferous hornblende, with crystalline andesine and a pale greenish-yellow epidote often intimately mixed with the feldspar, and so abundant as to characterize the rock. This epidote gave by analysis, silica 40·6, alumina 30-2, lime 17-7, protoxyd of iron 11.299.7.

3. Diorites, as already mentioned, sometimes contain albite. Associated with the Silurian ophiolites of Canada we often find beds of rock which are mixtures of albite with hornblende or pyroxene, sometimes with small portions of carbonates. These diorites are tough, granular, sub-translucent, greenish or bluishgray in color, weathering superficially to an opaque white and having a somewhat waxy lustre. Hardness 6-0; density 2·71— 2.76. The hornblendic element is sometimes nearly amorphous, but at other times forms cleavable grains; by ignition these portions become darker, while the feldspar is rendered whiter and more opaque, and often exhibits striæ upon the cleavage surfaces.

A fine grained variety of this diorite from Orford was examined; it had a somewhat yellowish-green color and a subconchoidal fracture. After ignition the striated crystalline grains of feldspar were distinctly seen. The powdered rock does not effervesce with nitric acid, which appears to be without action upon it. The analysis gave as follows:

*See R. H. Scott, L. E. and D. Phil. Mag., [4], xv, 518.