MINERALOGY. 



465 



Oryctogno- 



y- 



XV. The Frangibility. 



By frangibility is understood the resistance which 

 The Fran- minerals oppose when we attempt to break them into 

 gibility. pieces or fragments. It must not be confounded 

 with hardness. Quartz is hard, and hornblende com- 

 paratively soft, yet the latter is much more difficultly 

 frangible than the former. The degrees of frangibility 

 are the following. 1. Very difficultly frangible, aa in 

 native malleable metals, in silver-glance or vitreous 

 silver, and fine granular hornblende. 2. Difficultly 

 frangible, as hornstone and quartz. 3. Not particular- 

 ly difficultly frangible or rather easily frangible, as flint, 

 calcedony and copper-pyrites. 4. Easily frangible, as 

 opal, calcareous-spar, and fluor-spar. 5. Very easily 

 frangible, as straight lamellar heavy.spar, galena or 

 lead-glance, and slate coal *. 



XVI. The Flexibility. 



T be Fie*i- This term expresses the property possessed by tome 

 b iiny. minerals of bending without breaking. Flexible mine- 



rals are either elastical Jlexible, that is, if when bent 

 they spring back again into their former direction, as 

 mica; or common Jlexible, when they can be bent in 

 different directions without breaking, and remain in 

 the direction in which they have been bent, as mo- 

 lybdena, gypsum, talc, asbestus, and all malleable mi- 

 nerals. 



XVII. The Adhesion to the Tongue. 



^fc adne- This character occurs only in such minerals a* pos- 

 "* tbc sess the property of absorbing moisture, which causes 

 them to adhere to the tongue. It occurs principally in 

 soft and very soft minerals ; it is not known in hard 

 minerals, and there is but one instance of its occur- 

 rence in semi-hard minerals, that is, in the variety of 

 semiopal called ocvlus mundi. The degrees of adhe- 

 sion are, strongly adhesive, as meerschaum, and oculus 

 mundi ; pretty strongly adhesive, as bole, and potters 

 clay ; fetbly adhesive, as porcelain- earth, chalk, and 

 tripoli ; and not at all adhesive, as quartz and steatite. 



XVIII. The I'nctuosily. 



Tfce unctu- Some minerals feel greasy, others meagre; and in or- 

 eaity. der to distinguish the different degrees of greasiness, 



the following distinctions are employed. 



1. Very Girasy, as talc and graphite. 



2. (irraiu, as steatite and fuller's earth. 



3. Rather greasy, as asbestus and polished serpen- 

 tine. 



4. Meagre, as cobalt. 



Tbe greasy and very greasy minerals are generally 

 very soft and sectile, and become shining in the streak. 

 Mica feels smooth, but not greasy ; porcelain earth 

 feels soft and fine, but not greasy. 



tinguish artificial from true gems. It is, however, Oryctogne- 

 principally used in determining polished specimens. 'T- 

 The different degrees mentioned, are, ""Y"" 



I . Very cold. Examples, the precious stones, mer- 

 cury and agate. 



2. CM. Examples, Polished marble or limestone. 



3. Pretty cold. Examples, Serpentine, and gypsum 

 or alabaster. 



4. Rather cold. Examples, Coal and amber. 



XX. The Weight. 



The degrees of the gravity of minerals, according to Tht 

 Werner, are the following : weight. 



1. Swimming, or supernatant, which comprehends all 

 minerals that swim on water, and in which the 

 specific gravity is under 1000, water = 1000. 

 Example, Mineral oil, mountain cork, and mineral 

 agaric. 



2. Light, in which the specific gravity varies from 

 1000 to 2000. Examples, Amber, sulphur, and 

 black coal. 



3. Not particularly heavy, or rather heavy, in which 

 the specific gravity varies from 2000 to 4000. Ex- 

 amples, Quartz, flint, and calcedony. 



4. Heavy, from 4000 to 6000. Examples, Heavy 

 spar, copper-pyrites, and iron-pyrites. 



5. Uncommonly heavy, all minerals having a specific 

 gravity above 6000. Examples, Native metals, as 

 gold, silver, &c. ; ores, as galena or lead-glance, 

 tinstone, &-c. 



The first and second degrees, which comprehend the 

 swimming and light minerals, contain all the inflam- 

 mable minerals ; the third, with a few exceptions, all 

 the earthy minerals; the fourth, the greater number 

 of metalliferous compounds ; and the fifth, the native 

 metals and a few ores, &c. 



The preceding determinations answer very well for 

 the general Descriptions of species ; but it renders them 

 more complete when we ascertain the specific gravity, 

 by means of the hydrostatic balance. See the article 

 HYDRODYNAMICS, vol. xi. p. 429 456. for the mode of 

 conducting this experiment. 



Character* 



VI. CHARACTERS FOR THE HEARING. 



XXI. The Sound. 



The different kinds of sound that occur in the mine-The sound, 

 ral kingdom are the following: 1. A ringing sound, 

 which is a clear sound, as that of native arsenic, sele- 

 nite, and rock-crystal. Specimens to possess this pro- 

 perty in full perfection, should have one or two dimen- 

 sions, as length and breadth, greater than the thick- 

 ness : 2. A grating sound, which is a very weak rough 

 sound, resembling that emitted by dry wood, or fresh 

 burnt clay when rubbed, and is produced when the 

 finger is drawn across certain minerals, as mountain 

 cork and mealy zeolite : 3. A creating found, which is 

 a harsh sharp sound, as that of natural amalgam, when 

 pressed by the finger. 



VII. CHARACTERS FOR THE SMELL. 



Of this we can give no definition, and shall therefore Chancitn 



illustrate it by the minerals in which it occurs. for lht 



amelL 



Some earthy mineral*. >ueh at beryl, flint and opal, when first extracted from their native repositories, are more difficultly frangible 

 than after they hate been exposed for some lime to the influence of the atmorpbere. owing to their containing in these situations a consi- 

 derable portion of water, which being a nearly incompressible fluid, renders the mineral more difficultly frangible than it is after exposure 

 to the atmosphere, when the water has escaped, and the pores it occupied become ailed with air, which is a highly compressible substance. 

 ride Aikin, p. 9. 



TOL. XMT. TABT II. 3 X 



XIX. TheColdneti. 



Tke cold- When different kinds of minerals, all having equally 

 MI. smooth surfaces, are exposed for some time to the same 



temperature, we find by feeling them that they possess 

 different degrees of cold. To use this character with 

 precision much practice is required ; but those who 

 nave accustomed themselves to it, are able, by the mere 

 feel, to distinguish serpentine, gypsum, porphyry, ala- 

 baster, agate, Ac. from one another, and can also dis- 



