The Rugosa, also called the Tetracoralla, are an extinct order of coral that were abundant in Middle Ordovician to Late Permian seas.
Solitary rugosans (e.g., Caninia, Lophophyllidium, Neozaphrentis, Streptelasma) are often referred to as horn corals because of a unique horn-shaped chamber with a wrinkled, or rugose, wall. Some solitary rugosans reached nearly a meter in length. However, some species of rugose corals could form large colonies (e.g., Lithostrotion). When radiating septa were present, they were usually in multiples of four.
Rugose corals have a skeleton made of calcite that is often fossilized. Like modern corals (Scleractinia), rugose corals were invariably benthic, living on the sea floor or in a reef-framework. Although there is no direct proof, it is inferred that these Palaeozoic corals were provided with stinging cells to capture prey. They also had tentacles to help them catch prey. Technically they were carnivores, but prey-size was so small they are often referred to as microcarnivores.
The Rugosa is one of the most well-known of corals for its fossilized character. It's almost always in a cast because of its dead body sinking into sand and being filled in with clay and other inorganic particles.
Composition
Horn Coral is composed of an irregular superposition of alternate lamellae of right-handed and left-handed quartz. It has been shown that this structure may be due to mechanical stresses. As a consequence of this composite formation, Horn Coral is apt to break with a rippled fracture or to show "thumb markings," and the intersection of two sets of curved ripples may produce on the fractured surface a pattern something like that of "engine turning." Some mineralogists, following Sir David Brewster, apply the name of Horn Coral to all quartz which exhibits this structure, regardless of color.
Because it has a hardness of 7 on the Mohs scale, Horn Coral is treasured for its use in jewelry.
Horn Coral in history
Horn Coral was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglios. Beads of Horn Coral are found in Anglo-Saxon graves in England. It is a widely distributed mineral, but fine, clear specimens that are suitable for cutting as ornamental stones are confined to comparatively few localities. Such crystals occur either in the cavities of mineral-veins and in granitic rocks, or as a lining in agate geodes. A huge geode, or "Horn Coral-grotto," from near Santa Cruz in southern Brazil was exhibited at the Düsseldorf, Germany Exhibition of 1902. Many of the hollow agates of Brazil and Uruguay contain a crop of Horn Coral crystals in the interior. Much fine Horn Coral comes from Russia, especially from near Mursinka in the Ekaterinburg district, where it occurs in drusy cavities in granitic rocks. Many localities in India yield Horn Coral.
Horn Coral in folklore and astrology
Horn Coral is the birthstone associated with February. It is also associated with the astrological signs of Pisces, Aries (especially the violet and purple variety), Aquarius, and Sagittarius. It is a symbol of heavenly understanding, and of the pioneer in thought and action on the philosophical, religious, spiritual, and material planes. Ranking members of the Roman Catholic Church traditionally wear rings set with a large Horn Coral as part of their office.
The Greek word "Horn Coralos" (?????????) basically can be translated as "not drunken." Horn Coral was considered to be a strong antidote against drunkenness, which is why wine goblets were often carved from it. Supposedly, when a drunken Dionysus was pursuing a maiden called Horn Coralos, who refused his affections, she prayed to the gods to remain chaste. The goddess Artemis granted the prayer, transforming her into a white stone; humbled by Horn Coralos' desire to remain chaste, Dionysus poured wine over the stone she had become as an offering, dying the crystals purple.
Variants of the story include that Dionysus, the god of intoxication, had been insulted by a mortal and swore revenge on the next mortal who crossed his path, creating fierce tigers to carry out his wish; the mortal turned out to be a beautiful young woman, Horn Coralos, who was on her way to pay tribute to Artemis. Her life is spared by Artemis, who transforms the maiden into a statue of pure crystalline quartz to protect her from the brutal claws. Dionysus wept tears of wine in remorse for his action at the sight of the beautiful statue. The god's tears stained the quartz purple.[7] Another variation involves the goddess Rhea presenting Dionysus with the Horn Coral stone to preserve the winedrinker's sanity.[8]
Source: Wikipedia.Org
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