MARCASITE , a
See also:mineral with the same chemical composition as
See also:pyrites, being iron disulphide FeS2, but crystallizing in the orthorhombic instead of in the cubic
See also:system . The name is of Arabic origin and was long applied to crystallized pyrites (q.v.); it was restricted to the
See also:species by W . Haidinger in 1845 . The mineral was known to G .
See also:Agricola in 1546 under the names Wasserkies or Wesserkies and Leberkies, and it has been variously known as
See also:white pyrites, hepatic pyrites, lamellar pyrites, radiated pyrites (German Strahlkies) and prismatic pyrites . The orthorhombic
See also:form of the crystals, as distinct from the cubic form of pyrites, was recognized by Rome de l'Isle in 1772, though later R . J .
See also:Hauy considered the crystals to be only distorted cubic forms . The crystals are isomorphous with
See also:mispickel (q.v.), but only rarely are they distinctly
See also:developed and
See also:simple (fig.) . Usually. they are twinned on a prism
See also:plane, M, producing pentagonal stellate groups of five crystals; twinning on the plain g, in which the crystals intercross at angles of nearly 6o°, is less
See also:common . This frequent twinning gives rise to characteristic forms, with many re-entrant angles, to which the names "
See also:spear pyrites " and " cockscomb pyrites " are applied . The commonest state of aggregation is that of radially arranged
See also:fibres, the
See also:surface of the mass being globular, nodular or stalactitic in form .
Apart from crystalline form, the external characters of marcasite are very similar to those of pyrites, and when distinct crystals are not available the two species cannot always be easily distinguished . The
See also:colour is usually
See also:bronze-yellow, often rather lighter than that of pyrites; on freshly fractured surfaces of pure marcasite the colour is tin-white, but this rapidly tarnishes on exposure to air . The lustre is metallic and brilliant . The streak is greyish or brownish-black . The hardness (6–62) is the same as that of pyrites, and the specific gravity (4.8–4.9) as a
See also:rule rather less . Arsenical varieties of marcasite, containing up to 5% of arsenic, are known as lonchidite and kyrosite . Marcasite readily oxidizes on exposure to moist air, with the production of sulphuric acid and a white fibrous efflorescence of ferrous sulphate, and in course of
See also:time specimens in collections often became completely disintegrated . In nature it is frequently altered to
See also:limonite with the separation of native
See also:sulphur . Marcasite is thus the less
See also:stable of the two modifications of iron disulphide . Many experiments have been made with a view to determining the difference in chemical constitution of marcasite and pyrites, but with no very definite results . It is a noteworthy fact that whilst pyrites has been prepared artificially, marcasite has not . Marcasite occurs under the same conditions as pyrites, but is much less common .
Whilst pyrites is found abundantly in the older crystalline rocks and slates, marcasite is more abundant in
See also:clays, and has often been formed as a
See also:concretion around organic remains . It is abundant, for example, in the plastic
See also:clay of the
See also:Coal formation at Littmitz, near
See also:Carlsbad, in Bohemia, at which place it has been extensively
See also:mined for the manufacture of sulphur and ferrous sulphate . In the
See also:Chalk of the south-east of England nodules of marcasite with a fibrous radiated structure are abundant, and in the Chalk Marl between
See also:Dover and
See also:fine twinned groups of " spear pyrites " are common . The mineral is also met with in metalliferous
See also:veins, though much less frequently than pyrites; for example the " cockscomb pyrites " of the lead mines of
See also:Derbyshire and
See also:Cumberland . (L . J . S.) MARCEAU-DESGRAVIERS,
See also:FRANCOIS SEVERIN (176)–1796), French general, was
See also:born at
See also:Chartres on the 1st of
See also:March 1769 . His
See also:father was a
See also:law officer, and he was educated for a legal career, but at the age of sixteen he enlisted in the regiment of Savoy-Carignan . Whilst on furlough in
See also:Paris Marceau joined in the attack on the Bastille (
See also:July 14, 1789); after that event he took his
See also:discharge from the
See also:regular army and returned to Chartres, but the embarrassments of his
See also:family soon compelled him to seek fresh military enployment . He became
See also:drill instructor, and afterwards captain in the depart-
See also:mental (
See also:Loire) regiment of the
See also:National Guard . Early in March 1792 he was elected
See also:lieutenant-colonel of one of the battalions of the Eure-et-Loire; he took
See also:part in the defence of
See also:Verdun in 1792, and it fell to his lot to bear the proposals of capitulation to the Prussian
See also:camp . The spiritless conduct of the defenders excited the wrath of the revolutionary authorities, and Marceau was fortunate in escaping arrest and finding re-employment as a captain in the regular service .
Early in 1793 he became with other
See also:officers " suspect, " and was for some time imprisoned . On his
See also:release he hurried to take part in the defence of
See also:Saumur against the Vendean royalists, and distinguished himself at the combat of Saumur (
See also:June to, 1793) by gallantly rescuing the representative Bourbotte from the hands of the insurgents . The
See also:Convention voted him the thanks of the
See also:country, and thenceforward his rise was rapid . His conduct at Chantonnay (
See also:Sept . 5) won him the provisional
See also:rank of general of
See also:brigade . On the 17th of
See also:October he
See also:bore a
See also:great part in the victory of
See also:Cholet, and on the
See also:field of this
See also:battle began his friendship with Kleber . For the victory of Cholet Kleber was made general of division and Marceau confirmed as general of brigade . Their advice was of the greatest value to the generals in command, and the military talents of each were the complement of the other's . Marceau, who became general of division (Nov . 1o), succeeded to the chief command ad
See also:interim, and with his friend won important victories near Le Mans (Dec . 12–13) and Savenay (Dec . 23) .
After the battle of Le Mans, Marceau rescued and protected a
See also:young Royalist
See also:lady, Angelique
See also:des Mesliers . It is often supposed that he was in love with his prisoner; but the help even of the
See also:commander-in-chief did not avail to save her from the
See also:guillotine (
See also:Jan . 22, 1794) . Marceau had already retired from the war, exhausted by the fatigues of the
See also:campaign, and he and Kleber were saved from arrest and execution only by the intervention of Bourbotte . Marceau became affianced about this time to Agathe Lepretre de Chateaugiron, but his
See also:constant military employment, his broken
See also:health, and the opposition of the comte de ChMeaugiron on the one
See also:hand and of Marceau's devoted
See also:sister " Emira," wife of the Republican politician Sergent, on the other, prevented the realization of his hopes . After spending the winter of 1793–1794 in Paris he took a command in the army under Jourdan, in which Kleber also served . He took part in the various battles about Charleroi, and at the final victory of
See also:Fleurus (June 26, 1794) he had a
See also:horse shot under him . He distinguished himself again at Jiilich and at Aldenhoven, and stormed the lines of
See also:Coblenz on the 23rd of October . With the Army of the Sambre and Meuse he took his
See also:share in the campaign of 1795 on the Rhine and the
See also:Lahn, distinguishing himself particularly with Kleber in the fighting about Neuwied on the 18th and 19th of October, and at Sulzbach on the 17th of
See also:December . In the campaign of 1796 the famous invasion of Germany by the armies of Jourdan and
See also:Moreau ended in disaster, and Marceau's men covered Jourdan's retreat over the Rhine . He fought the desperate actions on the Lahn (Sept . 16 and 18), and at Altenkirchen on the 19th received a mortal
See also:wound, of which he died on the 21st, at the early age of twenty-seven .
The Austrians vied with his own countrymen in doing
See also:honour to the dead general . His
See also:body was burned, and- his ashes, which at the time were placed under a
See also:pyramid designed by Kleber, were transferred in 1889 to the
See also:Pantheon at Paris . See
See also:Maze, Le General Marceau (1889) ; Parfait, Le General Marceau (1892) ; and T . C .
See also:Johnson, Marceau (
See also:London, 1896) .
MARCANTONIO [MARCANTONIO RAIMONDI]
ETIENNE MARCEL (d: 1358)
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