Estimating Some Mechanical Properties Of Rock From In-situ Rebound Values
[A CASE STUDY OF OREKE OPEN PIT QUARRY]

L – type Schmidt hammer is also used to perform a test, the device is positioned normal to the rock surface  and the plunger (13) is pressed against the rock during which the reset spring (1) is pressed and the impact spring (6) is extended. At the end of the course, hammer holding lever (3), the hammer is released and after sliding along the plunger neck (11) hits the impact surface of the plunger (12). Based on the hardness of the rock surface onto which the plunger is pressed, the hammer rebounds and the amount of rebound is indicated by the number indicator (10) which is now moved upwards along with the rebound movement of the hammer.
2.2    GEOLOGICAL FORMATION OF MARBLE
    Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. When subjected to intense heat, pressure and chemical solutions, causing the stone to reform into an interlocking structure of calcite, aragonite and sometimes dolomite crystals.  Marble formed from very pure limestone is white, but the presence of other minerals, as well as clay, silt and sand, can give it richly varied coloration. (Kearey (2001).
    It is composed primarily of the mineral calcite (CaC03) and usually contains other minerals, such as clay minerals, micas, quartz, pyrite iron oxides, and graphite. Under the conditions of metamorphism, the calcite in the limestone recrystallizes to form a rock that is a mass of interlocking calcite crystals. A related rock, dolomitic marble, is produced when dolostone is subjected to heat and pressure. Marble is found in the mountainous regions of most countries, but relatively few quarries exist in the United States. (Philip, (2001).
Formation of marble
    Most marble forms at convergent plate boundaries where large areas of earth’s crust are exposed to regional metamorphism. Some marble also forms by contact metamorphism when a hot magma body heats adjacent limestone or dolostone. Before metamorphism, the calcite in the limestone is often in the form of lithified fossil material and biological debris. During metamorphism, this calcite recrystallises and the texture of the rock changes. In the early stages of the limestone to marble transformation, the calcite crystals in the rock are very small. In a freshly broken hand specimen, they might only he recognized as a sugary sparkle of light reflecting from their tiny cleavage faces when the rock is played in the light.