ENGLISH COLLECTION OF OUTSTANDING FOSSIL AND MINERAL SPECIMENS INFORMATION SHEET 5 (CASES 73, 74, 75) The three central cases (73, 74 and 75) in the main hall of the museum contain outstanding fossil and mineral specimens that are grouped according to various criteria, including exceptional preservation in the case of fossils, or size, brilliance, colour and/or extraordinary habit in the case of minerals. These properties render the specimens unique, and hence they are displayed separately from the general collections. This information sheet describes five each of the fossils and minerals exhibited in these cases.

CASE 73 CASE 73 CASE 74 CASE 74 CASE 74 SILICATES PHOSPHATES FISH REPTILES PLANTS

Beryl. is a relatively uncommon Vivianite is a rare mineral that is Priscacara was a fish belonging Mesosaurus was a reptile that lived Araucaria is a genus of coniferous mineral in nature, and transparent usually found as crystals measuring to the osteichthyes (bony fish) during the Permian, at the end of tree that remains extant today. It is crystals are even rarer. In these only a few millimetres in size. Larger group, and is equivalent to a the Palaeozoic. Its fossils have been named after Arauco, in Chile. The cases, the crystals can be cut to crystals like this one, measuring present day perch. Bony fish found exclusively in South Africa speciesmirabilis , to which the cone obtain precious gems that may be tens of centimetres, are extremely and South America, which led the displayed here belongs, is extinct. It account for nearly all the fish that green (emerald), yellow (heliodor) or rare. Normally, vivianite forms as a German scientist Alfred Wegener to is notable for its reddish colour, blue (aquamarine). In this speci- result of the destruction of other, we know and consume, such as speculate that these two continents which was caused by the conditions men, the aquamarine crystals form pre-existing minerals or in associa- hake, sea bream or sole. had been joined together in the of preservation: theAraucaria trees perfect hexagonal prisms embed- tion with concentrations of Priscacara originated in the past. Thus was born the theory of were buried by ash from a volcanic ded in a “mat” of mica (muscovite). phosphorus-rich organic matter. Mesozoic seas, but over the continental drift.Mesosaurus was eruption that occurred millions of This piece originally formed part of Although these crystals are now a course of its evolution it also small and had long jaws filled with years ago in what is now Argentine the wall of a miarolitic cavity (geodes dark greenish-blue colour, they began to occupy freshwater fine teeth. Its elongated, streamli- Patagonia. Over time, water filtered found in granitic pegmatites). were almost colourless originally. habitats. During the Eocene, it ned shape would have enabled it to into the sediments and precipitated The change has occurred because probably lived in streams and swim at great speed. minerals with red hues. Beryl (aquamarine) (Be Al Si O ). this iron phosphate is unstable and 32618 lakes, feeding on snails, crabs, Gilgit (Pakistan). has darkened over time. Mesosaurus brasiliensis. Araucaria mirabilis. Maximum dimension: 17 cm. prawns and tadpoles. Permian (270 million years ago). Jurassic (170 million years ago). Vivianite [Fe (PO ) ·8H O]. Sao Paulo (Brazil). Patagonia (Argentina). 3422 Priscacara sp. Anloua (Camerún). Maximum dimension: 40 cm. Maximum dimension: 9 cm. Maximum dimension: 21 cm. Eocene (45 million year ago). Wyoming (USA). Maximum dimension: 20 cm. ENGLISH COLLECTION OF OUTSTANDING FOSSIL AND MINERAL SPECIMENS INFORMATION SHEET 5 (CASES 73, 74, 75)

CASE 74 CASE 74 CASE 75 CASE 75 CASE 75 ARTHROPODS: TRILOBITES ARTHROPODS: CRUSTACEANS SILICATES SULPHIDES NATIVE ELEMENTS

The. trilobites are an extinct class of As with all the crustaceans, this Muscovite is perhaps the best Over 70% of stibnite, sometimes Although sulphur combines with arthropods that inhabited the extinct crab possessed a very hard, known phyllosilicate. It is a white, called antimonite, consists of oxygen and many metals, it can also Palaeozoic seas for almost 300 chitinous carapace. Its claws were silvery mica that is very common in antimony, but it also usually be found in its native state, as pure million years. As with present day very robust and generally of igneous and metamorphic rocks. It includes small amounts of gold, sulphur crystals. This large specimen arthropods, trilobites grew by different sizes. It had walking legs is characterised by marked basal silver, iron, copper and lead. The contains some excellent rhombic moulting their exoskeleton. As they on both sides of the body, but the cleavage, meaning that the flakes crystals form elongated prisms with crystals, and presents the yellow grew bigger, they tore and shed their existence of a fifth pair of flat hind easily come apart into thin sheets. longitudinal striations. It has a colour typical of sulphur. It can be external carapace, emerging head legs suggests that this crab was Thus, very thin and transparent metallic appearance and looks formed by the oxidation of sulphides first from the anterior region (i.e. the also able to swim. It was carnivo- sheets can be obtained that are hard, but in fact the crystals are very or by the reduction of sulphates, and cephalon). This specimen is an rous and is known informally as the often highly flexible. Formerly, delicate and soft (2 on the Mohs may also be induced by the biological example of a trilobite moulting, “mud crab”. It is thought that it was Muscovite was used for thermal scale). This specimen is notable for activity of certain organisms. illustrating displacement of the a deep water predator. insulation because it is a very poor its large size, the brilliance of its However, this specimen was cephalon as the trilobite emerges in conductor of heat. Consequently, it crystals and the unusual generated by volcanic exhalations, its new carapace. Archaeogerion peruvianus. was used in clothes irons to isolate arrangement of the prisms. which contain sulphur in the gases Neogene (15 million years ago). the hot plate from the handle, and in that are released by magma and rise

Isotelus maximus. Patagonia (Argentina). small stove windows. Its name Stibnite (Sb23 S ). through the Earth's crust. Ordovician (440 million years ago). Maximum dimension: 25 cm. comes from the former Russian Jiangxi (China). Ohio (USA). province of Muscovy, where large Maximum dimension: 20 cm. Sulphur (S). Maximum dimension: 17 cm. sheets of this mineral were Cattalnisetta (Sicily, Italy). extracted. The specimen displayed Maximum dimension: 32 cm. here is exceptional because it shows the hexagonal shape of the crystals, which grew on top of a feldspar aggregate.

Muscovite [KAl23 (SiAl) O 102 (OH) ]. Itinga, Minas Gerais (Brazil). Maximum dimension: 26 cm.