AUGITE. 



439 



Sulphate of strontium is celestine, the mineral which colours the blow-pipe 

 flame a fine crimson. There are certain varieties. Strontia salts are chemical 

 preparations. A beautiful pyrotechnic "red fire" is produced by mixing 

 nitrate of strontia with sulphur, antimony, charcoal, and chlorate of potassia.* 

 There is a carbonate of strontia in the same crystalline system. 



MAGNESIUM. With this metal we have a large group of minerals. 

 Magncsite is carbonate of magnesia, and occurs as talc-spar. The magnesium 

 limestone crystallizes as bitter spar. This dolomite is like 

 marble or common limestone, according to colour. Talc is 

 a combination of magnesia with silicic acid. The hydrated 

 carbonate is termed " white magnesia." The sulphate of 

 magnesia is found in Siberia, and we have boracitc, and 

 native magnesia called periclasc. The sulphate is generally 

 present in mineral waters, such as the Seidlitz and Epsom 

 Springs. Large masses have been found in the extensive 

 caverns of Kentucky and Tennessee, etc. Fig 463> _ Crystal of 



Meerschaum is a hydrated silicate of magnesia. It is 



found in Anatolia and Negropont, also in France and Australasia. Serpentine 

 is another similar composition. It is found in Cornwall, where it is carved 

 into various ornaments. It is sometimes called snakestone. There are 

 many other hydrated silicates of magnesia viz., gymnite, picrosmine, 

 pycrophyll, etc. 



There is another family allied to magnesia, called AUG1TES. These 

 minerals are black or dark-green, and are contained in lava and basalt. 

 AUGITE and HORNBLENDE are the chief representatives of this family. The 

 former crystallizes in the fourth system (see fig. 463), and there are several 

 varieties diallage, bronzite, diopsidc, etc. HORNBLENDE belongs to the 

 same system, and is a large factor in the composition of gneiss, syenite, 

 and porphyry. Tremclite is a 

 hornblende, and asbestos (amian- 

 tlws), and mountain-cork are also 

 varieties. The attribute of asbes- 

 tos for sustaining heat is well 

 known, and may be usefully em- 

 ployed for fire-proof purposes. 

 The well-known jade-stone of 

 China and calamity are other 

 varieties. 



ALUMINUM, OR ALUMI- 

 NIUM, gives us a large class of 

 minerals. It is the metallic 

 basis of alumina, which, com- 



* See " Strontium " in Chemistry. 



