Alumina

It has high percentage of silica and alumina.

Source: tatoeba (10915393)

Owing to the refractory nature of alumina it is with difficulty that it can be diffused in alkaline silicates, borates, or lead silicates.

Source: tatoeba (10935175)

As stated above, Gadolinite was discovered by Arrhenius in 1788. Geijer examined it in the same year, and described it as a black zeolite. In 1794 it was analysed by Gadolin, who declared it to be a silicate of iron, aluminium, and a new element which he called Ytterbium. In 1797 Ekeberg examined it, and confirmed the discovery. He proposed the name Gadolinite for the mineral, and Yttria for the new earth; these names were accepted by Klaproth, who examined it with Vauquelin in 1800, and by the French crystallographer Haüy. In 1802 Ekeberg showed that the oxide originally taken for alumina was in reality beryllia; in 1816 Berzelius showed that ceria was present with the yttria. About 1838 Mosander began his classical work on the earths in gadolinite. In that year he announced the separation of Lanthana, and in 1842 that of Didymia, which he had actually discovered eighteen months earlier. In the latter year he announced the separation of erbia and terbia. In 1842 also Scheerer declared that the yttria from gadolinite was a mixture of earths, from its different behaviour on heating in closed and open vessels; but when Mosander announced the discovery of didymia (the announcement appears to have been hastened indeed by Scheerer’s observation) it was agreed that the colouration observed was probably due to that earth. The further history of these earths must be continued elsewhere (vide p. 111).

Source: tatoeba (12209631)

The apocrenates of iron and manganese are slightly soluble; those of lime, magnesia and alumina are insoluble.

Source: wiktionary