The grouping together, under important and striking characters, common to them, the various and almost countless subjects in Natural History, has ever been admitted to be the only way in which an extensive knowledge of the Science can be acquired. It not only is the thread by means of which the interminable labyrinths of its study are explored, but it places before the student, those beautiful, instructive, and often curious analogies, contraries and coincidences, all of which it would be impossible to perceive without its assistance ; and enables him to form correct and useful generalizations; it allows him, in short, to collect and examine the gems and stalactites—the ores and other mineral productions in the cavern of Natural History —by keeping constantly in sight of the guide and his torch.

 

Some years ago, with a view to familiarize myself with the characters of minerals, and to discover some of the analogies, &c alluded to, I made various groups or tests of them, under different characteristic headings; a reference to which, it was likewise supposed, might assist me in determining the nature of a few of those I should meet with. It is not pretended that there is anything novel in this mode of arrangement, as various lists of minerals, bearing particular relation to their specific gravities, hardness, and colour, &c, have been printed. I only propose to offer you other lists, headed by other important and striking characters, common to the minerals in such lists; and, as there are not any more so than those which the application of heat discloses, it is further proposed to commence with them.

 

It is well known, that the immediate, or almost immediate effect of an elevated temperature upon some minerals, is to cause them to decrepitate, or fly into particles suddenly, with a crackling report, more or less violent—a phenomenon which may be regarded as the noisy boasting of the enemy, caloric, over his yielding antagonist, cohesion. Some minerals never fail to exhibit this character, before the blow-pipe or in the matrass, while in others it is capricious; but. as it is one which cannot be mistaken for another, and is, moreover, confined to a few minerals comparatively, a list will be presently introduced of those minerals which are said, by distinguished mineralogists, to decrepitate with heat, while opposite to every member in that list or table, will be affixed other characters, for the very obvious purpose of further distinction ; previously, however, a few observations are introduced upon the cause of decrepitation, and upon the mode of exhibiting, &c. Two causes have been assigned by chemists for the occurence of this phenomenon, viz.:—

 

First,—The sudden conversion into steam, by caloric, of the water which the minerals previously contained.

 

Second,—The unequal expansion of the laminæ, of which the minerals are composed, in consequence of their being imper¬fect conductors of heat.

 

Professor Ure, who adopts the latter opinion, criticises somewhat severely the former, and observes, that it is notorious, that some of those salts, which when absolutely dry, decrepitate most violently, contain no water whatever, and he instances, Sulphate of Barytes, Sulphate of Potass, and Muriate of Soda. Other mineral substances also, which decrepitate strongly with heat, contain no water; for instance, Fluor Spar, Glauberite, Chromate of Lead, Oxide of Tin, &c, and indeed, I the greater portion of those minerals which are described by mineralogists as decrepitatory with heat, have no water set down in their respective analysis.

 

Although these facts are directly opposed to the opinion, that I the presence of water is necessary in all, or even most cases, for I the development of decrepitation, there are cases, it would seem, in which its mechanical suspension in the mineral is necessary, before this phenomenon can be elicited. I have, at this moment, before me a mineral (a description of which is given at page 389, vol. II, Transactions Literary and Historical Society of Quebec,) which appears to be a compact variety of I either the Hydrate of Magnesia or Hydrate of Allumine, (Dr. Holmes, of Montreal, is of opinion, that it is a variety of Steatite). In a dry state it is slightly translucent on the edges, but being very hydrophanous, it becomes deeply so when absorbing water, in which state, upon being exposed to heat, either in the I matrass or on charcoal before the blow-pipe, it decripitates violently; but, previously to the absorption of water, no such character belongs to it. It is further remarkable and corroborative of the opinion, that water is the cause of decrepitation, in this instance, that this character may be renewed, at pleasure, in the same assay, by only moistening it, previously to subjection to heat. This fact, however, is by no means opposed to Dr. Ure's opinion as to the cause of decrepitation; because, it is highly probable, that the same mineral, which when dry, is a good conductor of heat, becomes the contrary when moist; and I believe, it will be found upon experiment, that other absorbent minerals which decrepitate when moist, lose that character upon becoming dry.

 

The phenomenon of decrepitation, is in general, best developed by directing the exterior flame of the blow pipe suddenly upon the assay, upon charcoal ; but different decrepitating minerals require often different degrees of heat; for, while some exhibit this character, only in the reducing flame of the blow pipe, others, to do the same, must be submitted to the more moderate temperature of the candle or matrass; whatever the degree of heat be however, it should always be applied suddenly, for, some of those minerals not subject to this law, may be made not to discover it, if they be heated gradually, a mode often adopted, when the fusibility of a mineral is the subject of enquiry, in which case decrepitation is a very inconvenient character. In ascertaining, whether decrepitation be a character belonging to a mineral, several trials, under different circumstances, should be made, for instance: in the candle, in the matrass, in the outer flame, in the reducing flame; and, when the mineral under examination, is absorbent or hydrophanous, it should be tried in both a moist and in a dry state, and in the description the particulars should be stated. It is obvious useless to continue the experiment with a fusing heat, or after the assay is red-hot, at which stages all decrepitation ceases.

 

It must be well understood, that in presenting to the Society the following Tabular View of Minerals which Decrepitate with Heat, it is not meant to assume, that a mineral which does not, cannot belong to one of the several species which it embraces, but only, that it probably does not; there are cases indeed, in which this probability almost amounts to a certainty; but the above general warning will not be the less necessary or that account. It must also be borne in mind, that the writer is not; compiling a System of Mineralogy, but arranging a few minerals, under certain heads, principally as an aide mémoire, in I doing which his main object, self improvement, will be realized, whatever opinion may be entertained of the general usefulness of his labours.

 

Wishing to have, as far is at was possible, an occular proof of | the approximate accuracy of these Tables, I have experimentally consulted as many of the minerals mentioned in them as are to be met with in the Cabinet belonging to the Literary and Historical Society; at least, whenever the specimens would admit of it, without injury to them. With reference to these Tables and experiments, I have ventured to mark in the former, with an asterisk, those minerals in which decrepitation may be considered sufficiently striking and constant to be characteristic. This experimental part of my labour would have been more satisfactory had I possessed the opportunity of consulting a larger cabinet, and, I trust, that great allowance will be made for this, or any other attempt which may succeed it, to be useful, while is is considered, that neither minerals, hooks, nor men, are very readily consulted in a country just commencing its scientific flight.

 

As they may not be found devoid of interest, although their perfect accuracy I will not guarantee, the experiments alluded to above, are here introduced:—

 

SUPHATE OF BARYTES

 

Of fourteen specimens of this mineral examined, twelve exhibited strong decrepitation. Of the two which failed one consisted of acicular prismatic crystals—the other was a fibrousty; compact variety, from Monte Paterno, near Bologna, (Bolognian Stone). Those in which this character was most striking were of a distinctly laminar or foliated structure.

 

CARBONATE OF BARYTES

 

One specimen, (the only one tried) slightly.

 

SULPHATE OF STONTIAN

 

Not one of seven specimens tried (four of them crystallized) can be considered as having decrepitated; the slightest, almost imperceptible motion, in some of them was alone observed. May not the presence of the Sulphate of Barytes give this character to this mineral when it exists?

 

ARRAGONITE

 

Three, of six assays from this mineral, decrepitated strongly. No signs of decrepitation in the others.

 

HYDRATE OF MAGNESIA AND MARMOLITE

 

Two specimens were tried, from the locality of Hoboken, New Jersey, neither of which succeeded; the presence of moisture might alter the case however, as it does with the specimen alluded to in the early part of this paper, and which resembling the Marmolite in appearance, is also found, to hold the same geological position, forming thin layers and thick seams in the serpentine and talcose schist of the Gannanoqui.

 

BRONZITE AND HYPERSTENE

 

Unsuccessful experiments.

 

FULLER’S EARTH

 

Decrepitation remarkably strong but single—one specimen tried.

 

CRYOLITE AND ALUMSTONE

 

No decrepitation in one assay of each—the fusibility, indeed, of the former is so great, that if ever it exhibits that character, and Berzelius stands alone as authority (first-rate however) that it does it must be at a very low temperature comparatively, as it melts in the flame of a candle.

The Metallic Minerals, submitted to experiment were the following, viz.:—

 

CARBONATE OF LEAD

 

All, of six crystallized specimens, decrepitated strongly.

 

SULPHURET OF LEAD

 

Only five, of ten assays, decrepitated; these did so, however, strongly—one was crystallized in cubes—two granular, and two massive (laminarly): those deficient in this character were, three, massive—one, granular (argentiferous)—and one, crystallized in octohedra.

 

MOLYBDATE OF LEAD

 

The only two specimens tried decrepitated strongly; they were crystallized in flat octohedra (much flatter than the primary) and in very low right square prisms—Sheperd.

 

CHROMATE OF LEAD

 

Also two specimens—strongly; both crystallized, one in rhombic prisms of 93° 30' and 86° 30'—Sheperd.

 

PHOSPHATE OF LEAD

 

Three, of four specimens decrepitated, two of them crystallized in six-sided prisms, and one in acicular and radiating crystals—the former strongly—the latter slightly. A brown Phosphate of Lead, in six-sided prisms, apparently corroded, did not decrepitate.

 

OXIDE OF TIN

 

The only specimen tried (under the usual form of crystal) very strong.

 

SULPHURET OF ZINC.

 

Five, of six assays, all from crystallized specimens, decrepitated. The specimen in which this character was not observed is a fibrous blende.          

 

ELECTRIC CALAMINE

 

No decrepitation in the two specimens tried.

 

CARBONATE OF IRON

 

Four, out of five, strongly; both crystallized and massive— the fifth was "in distinct crystals of the primitive form."—; Sheperd. Among an equal number of primary and secondary crystals of the same decrepitating mineral would not the character appear more frequently in the latter than the former?

 

WOLFRAM

 

Three, out of four—two crystallized (laminarly) and one compact (the last most violently); the fourth was granular.

 

TUNGSTATE OF LIME

 

One specimen (crystallized in octohedra) slightly—the only, one tried.

 

COPPER PYRITES

 

Four specimens tried, decripitated—three of them strongly (two crystallized, one compact); the fourth (botryoidal) slightly.

 

GREEN CARBONATE OF COPPER      

 

Of four specimens, the only crystallized one (a circumstance unusual) among them, did not decrepitate.

 

It will be found in general, that a mineral which decrepitates possesses either a crystallized form or a crystalline structure; most frequently. Among fibrous minerals the character is some what rare, and still more so among such as are of an earthy texture. Fullers' earth is a striking exception to the latter assertion, but it must be remembered, that its texture is quite as compact as it is earthy, and an analagous observation may lie made respecting the Green Carbonate of Copper, the structure of which is very compact as well as fibrous. Granular Mnerals often exhibit decrepitation, but they are obviously, in general, composed of an assemblage of small crystals—from all of which it appears, that in collecting an assay for examination in this particular character, the most crystalline portion of the mineral should be taken, and particularly such portion the structure of which is laminar.

 

In compiling this paper, all the works on the subject I could meet with have been consulted, viz.: Berzelius, Bakewell, Cleaveland, Griffin, Mohs, Jameson, and Phillips. A few, a very few, of the observations are original, at least, as far as the writer's information extends. Should the whole prove acceptable, his labours will be continued on the same plan. Among the distinguished works on Mineralogy just named, not one holds a higher place than Cleaveland's, at once remarkable for its fulness of detail, and for its perspicuity of style. It is a treatise I have always had recourse to in my mineralogical difficulties, and the student will find it, as I have, the Pharos, I which if it do not always conduct to port, will, at least, save; him from being wrecked upon the shoals and quicksands of the Science. If he be an American, two additional motives are his to possess it, as it is a work of which he may be justly proud, and the only one which offers him a compendium of § the Mineralogy of his country[1].

 

 

The preceding Tables were intended to be the first of a Series, embracing the leading characteristics of Minerals, arranged in a similar manner;—the value of such a Guide to the Student of Mineralogy has already been touched upon. Unfortunately, however, CAPTAIN BADDELEY was called from Quebec, before he could carry his intentions fully into execution—and the increasing claims of duty, consequent on the distracted state of the Province, during some years, and his subsequent departure, for India, put it out of his power to resume his work. The SOCIETY have, however, deemed it right to give these Tables a place in their TRANSACTIONS, both from their intrinsic value, as far as they go, and as the latest Work of one, who, while in the Province, laboured long and zealously in the field of Canadian Geology and Mineralogy, as the preceding Volumes of their "Transactions" amply testify.