304 NEW ZEALAND NATURE-STUDY BOOK 
suitable specimens. From these a few typical ones should 
be selected for investigation. The non-crystalline varieties 
are best to begin on, though the harder crystalline rocks 
_ should certainly be examined. 
Note the colour of the specimens, and compare with 
calcite. HKduce the characteristic white appearance they all 
present—-test for hardness, and if several specimens 
are available for examination, determine which variety is 
hardest. Taking one of the specimens, observe its texture 
—make out that it is either crystalline or composed of 
small particles more or less firmly held together, 
Test for cleavage and fracture. The former will most 
probably be absent—the latter may be uneven, splintery, or 
conchoidal. Notice that it is much more brittle than 
most of the volcanic rocks dealt with—more easily broken, 
and more easily reduced to powder. Examine carefully 
both the outside surface of the specimens and the material 
scraped off with a knife, and notice if any small shells or 
other organisms are to be seen. These, though they 
cannot be seen in the mass itself, are often visible on the 
weathered surface. By selecting a few suitable specimens, 
the organic origin of the rock can be made clear. 
Test for taste and odour; and determine specific 
gravity. Pour a few drops of dilute Hydrochloric Acid on 
a clean surface and observe the effervescence; heat the 
acid and again apply—notice the increased violence of the 
re-action. Powder up a small quantity of the rock and 
drop into a test tube, cover with acid—notice (if the rock 
be pure) that the whole of the material will disappear. 
Limestone effervesces when acid is poured on it 
—and is soluble in acid. Pure Limestone is composed 
of Carbonate of Lime—i.e., of Carbon-dioxide and Lime 
chemically united. When ae apphed, the Carbon- dioxide 
is liberated ; hence the effervescence. 
