XIV. Chemical Examination of, and Remarks on, the Mineral Species Tyrite. By D. FORBES, F.G.S., F.C.S., A.I.C.E.*

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'N Poggendorff's Annalen der Physik und Chemie, 1856, No. 4, p. 622-628, is inserted a communication from M. Kenngott of Vienna, entitled "Notiz über das Tyrit genannte Mineral," in which the author makes some remarks on the crystalline form of that mineral, and institutes a comparison between it and the Greenland mineral Fergusonite, from which he concludes that both these species are identical.

Before making any observations on this question, I am enabled to bring forward a chemical examination of the mineral from the same locality as those examined crystallographically by M. Kenngott, and received from Dr. Bondi of Dresden.

The species is Norwegian, and obtained from the large felspar quarry at Helle at Næskül, about ten English miles east of Arendalf, where the mineral occurs pretty abundantly, and occasionally in crystals above 2 inches in length.

These crystals invariably have their bases attached to plates of black mica, and shoot out thence, imbedding themselves in the red orthoclase, which very frequently forms thin plates or slabs of from of an inch to 4 inches in thickness, bounded on both sides by the black mica.

The annexed woodcut gives an idea of this mode of occurrence.

The minerals associated are orthite, alvite, ametallic mineral containinguranium, uranium ochre, and a new mineral of a brown-red colour not yet analysed.

In none of the very numerous crystals I have obtained are the angles otherwise than extremely uneven and indistinct, having often a rounded or compressed appearance, and are almost always pyramidal, running off to a point without any distinct facets. Not the slightest degree of reliance could be put upon measurements obtained by the hand-goniometer. They present a quadrilateral section, and are probably tetragonal, having one distinct cleavage plane, and traces of two others. The fracture, cleavage, and colour are so different from those of the original Tyrite from Hampemyr on Tromoe, that, until after the present analysis was made, it was considered uncertain whether they were the same mineral,

* Communicated by the Author.

There is a mistake in the locality as given by M. Kenngott; Helle being on the mainland at Næskül, and not on the Island of Tromoe. A section of this quarry will be found in the Quarterly Journal of the Geological Society of London, May 1855, Dr. Bondi's specimens were, I believe, collected by Zschau of Dresden.

-The colour varies from a grayish-brown to a rich clove-brown; streak yellowish-brown; glance resinous to semi-metallic. In small splinters translucent.

Hardness 6'5, being capable of scratching orthoclase. Brittle. Fracture splintery up to subconchoidal.

"Fragments of the crystals heated to redness in a tube decrepitate, and evolve water, becoming at the same time of a fine greenish-yellow colour. Dissolves in borax to a glass, which is brownish-yellow whilst hot, becomes green under cooling, and when cold is greenish-yellow. With microcosmic salt leaves a residue undissolved, and gives a glass which is yellow whilst hot, and becomes green on cooling. aastal para

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The specific gravity of a fragment possessing cleavage planes was found to be 5-36; another fragment more conchoidal in fracture gave 5.13; both specimens being pure.

The specimen chosen for analysis had the cleavage planes better expressed than usual, and was perfectly free from intermixture. When finely powdered it was of a gray-brown colour, and on ignition lost weight, becoming of an umber-yellow colour.

The powder was decomposed by boiling with concentrated sulphuric acid in a platinum vessel; the columbic acid which remained undissolved being washed and determined, it became of a fine citron-yellow colour on heating, but when cold had recovered its original white colour.

The solution was rendered alkaline by ammonia, and oxalic acid then added until the solution reacted slightly acid. The precipitated oxalates were collected and ignited, when they appeared of a faint whitish-yellow colour without a trace of brown, so that probably little or no didymium was present.

They dissolved readily and completely in hydrochloric acid, and this solution was precipitated by ammonia and filtered off. Lime was determined, as usual, in the filtrate by precipitation as oxalate. No magnesia was found.

The precipitate containing only yttria, with the oxides of cerium and lanthanium, was redissolved in a little sulphuric acid and boiled with a concentrated solution of sulphate of potash, thus separating the ceric oxides, which were filtered off, dissolved in hydrochloric acid, precipitated by potash, redissolved in hydrochloric acid, precipitated by ammonia, and determined; they were then converted into nitrates, ignited, and the lanthanium separated by digestion in a solution of chloride of ammonium and determined.

The yttria was precipitated from its solution in sulphate of potash by caustic potash, dissolved in hydrochloric acid, reprecipitated by ammonia and determined. sor

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The original solution from which the oxalates had been sepa

rated was now precipitated by hydrosulphate of ammonia and filtered. The filtrate showed a trace of tin, which was not estimated; the precipitate contained alumina, iron, uranium (glucina ?), and an earth which was probably zirconia, although its oxalate was soluble. The alumina was separated by boiling the whole in caustic potash and determined as usual. Iron was then separated by carbonate of ammonia, and the solution, containing then only zirconia (glucina ?) and uranium, precipitated together and determined after ignition; the uranium was then dissolved out by hydrochloric acid, and determined as difference of weight between the residue insoluble in acid and the former combined amount.

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The oxide of iron was determined as usual, but on being redissolved contained some insoluble earth, which was deducted from its weight and added to the amount of zirconia. The quantities thus found were as follow:

Water mean of four determinations as
loss on ignition

Columbic acid obtained

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4.66 per cent...

25.04 grains.

11.12...

B

Mineral employed in analysis

Ignited oxalates obtained

which, when tabulated, will afford the following per-centage

The atomic equivalents of several of these bodies being so

uncertain at present, it would be only guesswork to attempt deducing a formula; but it will be at once seen from the above analysis, that the mineral from Helle is identical with the Tyrite from Hampemyr on the Island of Tromoe, described in the New Edinburgh Philosophical Journal, No. 1, 1855.

With regard to the mineral Fergusonite, from Kikertaurvak near Cape Farewell in Greenland, our information at present rests upon Haidinger's crystallographic examination (Edinb. Roy. Soc. Trans. vol. x. p. 274), Berzelius's blowpipe reactions, and Hartwall's chemical analysis, both in the Kongl. Vetenskabs Academiens Handlingar for 1828, p. 167, to which M. Kenngott has not brought forward any addition; and not having seen any specimen of that mineral, I must refer entirely to these authorities.

The comparison of the two minerals instituted by M. Kenngott rests upon

1. Their crystallographic identity. But the crystals of Tyrite hitherto found are so extremely uneven and irregular, as before mentioned, that no dependence can be placed upon measurements of their angles by a hand-goniometer; and quite as many discordant results could be adduced to meet those cited by M. Kenngott. There seems, however, much probability that the crystalline form will prove the same, but this is not so certain as to set

the matter at rest.

2. Resemblance in physical properties. These present several points of unquestionable agreement; the colour, glance, and streak must be pretty nearly the same. The hardness of Tyrite is probably but very little higher, all specimens I have tried scratching orthoclase, and being about 65; Fergusonite being stated as 5.5 to 6.0. The specific gravity of Tyrite is, however, decidedly lower than that of Fergusonite, which is stated as 5.838 (Allan), and 5.800 (Turner); whereas the mean of a number of determinations of the specific gravity of specimens of Tyrite, both from Helle and Hampemyr, was 5'33, and only one specimen was found to be above 5.36. All the specimens were perfectly pure, any decomposed or weathered parts being carefully removed if present.

3. Similarity of blowpipe reactions. As the action of fluxes on these minerals depends chiefly on the presence of uranium, they both react with borax and microcosmic salt similar to most minerals containing this metal.

According to Berzelius and Hartwall, Fergusonite only evolves a trace of water when heated in a tube, whereas Tyrite decrepitates often very strongly and evolves considerable water.

4. Chemical composition and constitution are best seen from the following tabulated statement:

From this it will be seen that there is a very considerable difference in the amounts present of the various elements. In Fergusonite Berzelius and Hartwall found a trace of water, consequently were not ignorant of its existence, so that M. Kenngott cannot with propriety refer to this with the remark, " dass man sie gar nicht fand, wenn man sie nicht suchte;" and if he consulted the original memoir of M. Hartwall, he has quite forgot to insert in his communication M. Hartwall's observation, that we may with certainty regard water as not entering into the chemical constitution of Fergusonite*.

There can be no doubt as to the water in Tyrite being essential to its constitution; and the determination of water as given in the analyses is probably below the real amount, as the mineral appears to oxidize on heating, which makes the loss less than it otherwise would be; for this reason, it was found that the amount of water was greater when the mineral was heated in fragments than when heated in powder, and the length of time also was of importance.

When well crystallized, the mineral on heating decrepitated often very strongly, and on losing its water sometimes suddenly fell entirely to powder, having a fine greenish-yellow colour.

Many determinations were made of the water, and the average of all was 4.80; but this is probably too low, as several of them were made on the finely powdered mineral heated for a considerable time, and which consequently showed less than otherwise.

The differences in the quantities of the other elements is at once seen by reference to the tabulated results. It is not,

Kongl. Vet. Acad. Handl. 1828. p. 170.