Gem-A Authorized Training Center - Corsi di gemmologia
IGL - Istituto Gemmologico Ligure

Istituto Gemmologico Ligure

Gem-A Accredited Teaching Center

La struttura del corallo


il libro che parla dei coralliThe microstructural components of the [CaCO.sub.3] skeleton from a wide range of scleractinian corals have been well documented (see Wainwright, 1963; Vahl, 1966; Sorauf, 1970, 1972, 1974, 1980; Wise, 1970, 1972; Chevalier, 1974; Jell, 1974; Constantz, 1986, 1989). However, descriptions of skeletal microstructure are inconsistent, reflecting differences in both interpretation and structural variation. The relationships between the various crystalline microstructures found on the surface and within the interior of the skeleton are not fully understood, although this is fundamental to an understanding of the origin of crystal formation, deposition and growth.

The basic structure of the coral polyp is a tubelike skeleton, or corallum, divided by longitudinal and horizontal partitions. Sitting in the top of this tube is the living polyp. The key elements of the corallum are the longitudinal divisions, the septa, which are joined laterally by the wall (theca) of the corallum. Those septa that extend above the top of the theca are referred to as exsert septa. Exsert septa are one of the primary sites of [CaCO.sub.3] deposition and skeletal extension in the scleractinian coral Galaxea fascicularis (Marshall and Wright, 1998). These elongated septa protrude upward from the wall of the corallite and encircle the oral disc (see Fig. 1). This arrangement allows for individual septa to be easily detached from the corallite, without significant damage, for subsequent investigation of the crystalline microstructure with scanning electron microscopy (SEM).


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