Alongside stalactites and stalagmites are a profusion of rare speleothems: aragonite
crystals, coral-like shapes, exuberant helicites, long soda straws, twisted candlesticks.
If the mollusc is unable to get rid of the irritant, as part of its defence mechanism it produces conchiolin (an organic glue) and nacre (calcium carbonate crystallised in the form of aragonite
The presence of a strange body (a grain of sand or a cestode or trematode larva) causes the mantle of the oyster to produce concentric protective layers of a scleroprotein called conchiolin, and calcium carbonate in the form of aragonite
. The mantle epithelium invaginates and forms the so-called pearl sac, around which the pearl grows.
Corbulid shells characteristically contain within each valve at least one conchiolin layer that is accreted simultaneously with other microstructural layers (made of aragonite
crystals and organic matrix) throughout most of the bivalve's life [ILLUSTRATION FOR FIGURE 2 OMITTED].
Several basic crystal forms of calcium carbonate are found, the most common being calcite and aragonite
. Dolomite and vaterite, which are very unstable, also occur naturally.
X-ray diffraction analysis demonstrated the presence of aragonite
and opal within Celtis occidentalis endocarps.
The diagenetic fabric of the Lockhart Limestone is characterized by several diagenetic features such as micritization, neomorphism (aragonite
to calcite transformation and development of microspar), compaction, pressure dissolution (microstylolites) and cementation (calcite filled microfractures).
We used carbonate seed crystals of four kinds: calcite, aragonite
, dolomite, and magnesite.
Heliopora coerulea is the only species in the subclass Octocorallia that has a crystalline aragonite
2B) were measured and recorded, but the diameter of the circle at the upper point of the inner layer of the aragonite
nacre (UND, Fig.
Their shells may consist of naturally formed biogenic CaC[O.sub.3] which exist in several crystallographic polymorphs such as calcite (R-trigonal), aragonite
(Porthorhombic), and vaterite (P-hexagonal) [1, 2].