Corsi Collection of Decorative Stones

Class IX
Basalts (Basalti)

Basalt used to be called pietra di ferro by the ancients, since it was confused with very finely grained granite that merited such a name. It is however a volcanic product that generally is presented in the form of columns and pilasters. It is of a compact texture, tough, and very hard, in which no foreign substance is found. It can barely be worked, and takes a polish with difficulty.

Basalt is a dark, fine-grained, volcanic rock, which sometimes cools to form dramatic polygonal columns. The so-called basalti antichi, however, are not true basalts, but metagreywackes; greywackes, poorly sorted sedimentary rocks composed mainly of sand, grit and clay, that have undergone metamorphism. According to Del Buffalo i , the name basalti is thought to have arisen from the erroneous reading in Pliny of 'basalten' for 'basanitem'. The Italian name has given rise to misunderstanding for many years. See Gnoli ii for a history of this. None of Corsi's specimens in this class are what geologists would call basalt.

Fine-grained black 'granites' were sometimes called pietra di ferro or pedro e' ferru because they resembled dark ironstones in appearance.

i. Del Bufalo (2002) 200
ii. Gnoli (1988) 112-116

§ I Ancient basalts (Basalti antiche)


671. (160.1) Pietra di paragone. Marmor Lydium. Authorities agree that Lydian stone (pietra lidia) corresponds to touchstone. Indeed Pliny 95 says that the Lydian stone is a type of basalt used for testing gold. In colour it is consistently black; it used to be found in Lydia, a province of Asia Minor. There is a beautiful urn of this stone under the High Altar of the Church of S. Croce in Gerusalemme. (Very rare).

Corsi appears to have cited the wrong reference in Pliny here, to 'magnes' (the magnet) rather than to touchstone; about which Pliny i writes:

'A description of gold and silver is necessarily accompanied by that of the stone known as “coticula.” In former times, according to Theophrastus, this stone was nowhere to be found, except in the river Tmolus, but at the present day it is found in numerous places. By some persons it is known as the “Heraclian,” and by others as the “Lydian” stone. It is found in pieces of moderate size, and never exceeding four inches in length by two in breadth. The side that has lain facing the sun is superior to that which has lain next to the ground. Persons of experience in these matters, when they have scraped a particle off the ore with this stone, as with a file, can tell in a moment the proportion of gold there is in it, how much silver, or how much copper; and this to a scruple, their accuracy being so marvellous that they are never mistaken.'

i. Pliny 33.43, tr. Bostock & Riley (1855)

672. (160.2) Basalte scura. Marmor Aethiopicum. Although another black basalt similar to the above might have been be found in Ethiopia, nonetheless rarer and more beautiful than all was this dark one, very similar to the colour of coffee. The only known example of this stone is one small Bacchus lying in the Galleria de' Candelabri of the Vatican Museum no.1385,[p161] and which can be seen restored with green basalt, which demonstrates that such stone would be (rare).

673. (161.3) Basalte verde. This stone is absolutely monochrome, and of a dark apple green. In the octagonal courtyard of the Vatican Museum there is of this stone a large and beautiful water container, or it might be a bath. (Very rare).

674. (161.4) Basalte listata. This basalt is composed of the two above basalts inasmuch as the ground is green, and the stripes are the colour of coffee. (Very rare).

675. (161.5) Basalte fiorita. It has a green ground covered all over with small whitish spots. (Very rare).

§ II Italian basalts (Basalti d'Italia)

676. (161.1) Basalte di Venezia. Very deep apple green all over, with some scarcely visible black spots. (Rare).

677. (161.2) Another of a little lighter green, with white and faded yellow veins. (Less rare).

678. (161.3) Basalte di Bolsena. Black ground with waves of dusky grey. (Common). 96