428 KANSAS CITY RE VIE IV OE SCIENCE. 



aragonite, or dendritic (tree-like) shapes, as magnetite (magnetic iron ore). Other 

 species occur as stalactites or stalagmites, as limestone. 



There are also many other imitative shapes in which minerals are found, 

 such as amygdaloidal, (almond-shaped,) reniform, (kidney-shaped,) capillary, 

 {resembling a thread or hair,) reticulated, (net-like,) acicular, (resembling a needle,) 

 etc. In short, a careful examination of the general structure and imitative shape, 

 if any, of a mineral, will often lead to its identification without further trouble. 



8. There are various other physical characters of minerals, such as magnet- 

 ism, taste, odor, feel, tenacity and phosphorescence, that are often useful in their 

 determination. For instance, magnetite can be distinguished from minerals which 

 it otherwise resembles by its property of being attractable by a magnet, or mag- 

 netized knife-blade; native alum by its astringent taste; kaolin or clay by its 

 peculiar odor; and the hydrous silicates, — talc, serpentine, and chlorite, by their 

 smooth or greasy feel. When two pieces of quartz are rubbed against each other 

 they will emit light, or are phosphorescent. This is best seen in the dark. 



The determination of the physical characters of minerals is, generally speak- 

 ing, sufficient for the identification of all common, and also many uncommon, 

 species, but there are many others that need to be tested chemically before their 

 identification is rendered certain. This treatment is also necessary when the 

 chemical composition of a mineral is to be ascertained, or the exact proportion of 

 metal in an ore of silver, lead, copper, etc, determined. This latter process is 

 called assaying. 



We will now speak of the chemical characters of minerals. 



Treating the mineral with acid is usually the first step. Calcite or common 

 limestone can be readily recognized by its lively effervescence when touched with 

 hydrochloric (muriatic) acid, while in the mass, but dolomite or magnesian lime, 

 stone will only effervesce when powdered. Other minerals require the use of 

 strong or hot acid. In addition to hydrochloric, sulphuric and nitric acids are 

 often used. By the employment of acids the degree of solubility is determined, 

 the presence of carbonic acid detected, and various other results obtained. After 

 treatment with acids come the blow-pipe tests. The mineral is placed upon char- 

 coal and submitted to the action of the flame of an alcohol lamp or gas jet directed 

 upon it by the blow-pipe. The degree of fusibility is noticed, the color of the 

 flame noted, and also the character of the sublimates, and the odor of the escap- 

 ing gases. The mineral is heated in open and closed glass tubes, and then 

 mixed with the fluxes, soda, borax, and salt of phosphorus. By these and other 

 methods of treatment, and reference to a set of tables on the determination of 

 mineral species, the exact status of the specimen in hand is finally decided. 



The quantitative analysis of minerals, by which the precise proportion of 

 each of their chemical constituents is found, requires a still more careful examin- 

 ation and additional treatment. A few words on the identification of rocks will 

 not, perhaps, be out of place. To ascertain the peculiar species to which a rock 

 belongs, it is only necessary to identify its constituent minerals, as, if we find a 

 rock to consist of an aggregate of the minerals quartz and orthoclase promiscu- 



