GOTHITE, or Goethite, a mineral composed of an iron hydrate, Fe203.H20, crystallizing in the orthorhombic system and isomorphous with diaspore and manganite.
Crystals of barytes are orthorhombic and isomorphous with the strontium and lead sulphates (celestite and anglesite); they are usually very perfectly developed and present great variety of form.
Magnesium sulphate (orthorhombic) takes up ferrous sulphate (monoclinic) to the extent of 19%, forming isomorphous orthorhombic crystals; ferrous sulphate, on the other hand, takes up magnesium sulphate to the extent of 54% to form monoclinic crystals.
By plotting the specific volumes of these mixed crystals as ordinates, it is found that they fall on two lines, the upper corresponding to the orthorhombic crystals, the lower to the monoclinic. From this we may conclude that these salts are isodimorphous: the upper line represents isomorphous crystals of stable orthorhombic magnesium sulphate and unstable orthorhombic ferrous sulphate, the lower line isomor phous crystals of stable monoclinic ferrous sulphate and unstable monoclinic magnesium sulphate.
They all crystallize in the monoclinic system, often, however, in forms closely resembling those of the rhombohedral or orthorhombic systems. Crystals have usually the form of hexagonal or rhomb-shaped scales, plates or prisms, with plane FIG.
When crystallized from water, crystals belonging to the orthorhombic system, and having a prism angle of 61 0 10', are obtained; they are often twinned on the prism planes, giving rise to pseudo-hexagonal groups resembling aragonite.
The salt crystallizes out on cooling with 7 molecules of water, forming colourless orthorhombic prisms, usually small and needle-shaped.
The crystals are orthorhombic, with angles similar to those of marcasite; they are often prismatic in habit, and the prism M is usually terminated by the deeply striated faces of an obtuse dome r.
This variety forms a passage to the species glaucodote, (Co,Fe)AsS, which is found as well-developed orthorhombic crystals in copper ore at Hakansboda in Ramberg parish, Vestmanland, Sweden.
Other species belonging to this isomorphous group of orthorhombic minerals are marcasite (FeS2), lollingite (FeAs 2), safflorite (CoAs2) and rammelsbergite (NiAs 2).
MARCASITE, a mineral with the same chemical composition as pyrites, being iron disulphide FeS2, but crystallizing in the orthorhombic instead of in the cubic system.
The orthorhombic form of the crystals, as distinct from the cubic form of pyrites, was recognized by Rome de 1'Isle in 1772, though later R.
Hot or dilute cold solutions deposit minute orthorhombic crystals of aragonite, cold saturated or moderately strong solutions, hexagonal (rhombohedral) crystals of calcite.
Epsom salts crystallizes in the orthorhombic system, being isomorphous with the corresponding zinc and nickel sulphates, and also with magnesium chromate.
The compound FeS 2 is dimorphous, and the modern practice is to distinguish the cubic forms as pyrites and the orthorhombic as marcasite (q.v.).
There is reason to suppose that the change described takes place in two stages, the gypsum first forming orthorhombic crystals and then crystallizing in the monosymmetric system.
Correlatively in its process of dehydration to form plaster of Paris, monosymmetric gypsum is converted into the orthorhombic form before it begins to be dehydrated.
Codeine, or codeia, crystallizes in orthorhombic prisms with one molecule of water: it is readily soluble in alcohol, ether and chloroform.
Silver sulphide, Ag 2 S, occurs naturally as the orthorhombic acanthite, and the cubic argentite; the telluride, Ag 2 Te, named hessite, assumes cubic forms; other tellurides containing silver are petzite, (Ag,Au) 2 Te, and sylvanite, AuAgTe 4.
Phosphorus tetroxide, P204, was obtained by Thorpe and Tutton by heating the product of the limited combustion of phosphorus in vacuo as a sublimate of transparent, highly lustrous, orthorhombic crystals.