Genitive of Quality, Description, or Characteristic is used only when the quality is modified by an adjective. The genitive of quality is much less common in classical prose than the ablative of quality. In general the genitive of quality is used of essential, the ablative of quality of special or incidental characteristics. [A&G 345]
Erat sane somni paratissimi, non numquam etiam inter ipsa studia instantis et deserentis. [Pliny III.5]
Quorsus haec? ne tibi, optimae indolis iuveni, quorundam in mensa luxuria specie frugalitatis inponat. [Pliny II.6]
Fuit moris antiqui eos qui vel singulorum laudes vel urbium scripserant aut honoribus aut pecunia ornare .... [Pliny III.21]
Expressions such as eius modi, cuius modi are genitive of quality.
Sic candidatum me suffragio ornavit, sic ad honores meos ex secessibus accucurrit, cum iam pridem eiusmodi officiis renuntiasset, sic illo die quo sacerdotes solent nominare quos dignissimos sacerdotio iudicant me semper nominabat. [Pliny II.1]
The genitive of measure is a type of genitive of quality used with numerals.
Esse autem tibi centum milium censum satis indicat quod apud nos decurio es. [Pliny I.19]
Another variety of the genitive of quality is the genitive of price or value (cf also the genitive of charge or penalty with verbs of accusing, condemning or acquitting).
Rogo cures quanti aecum est emat: ita enim delectabit emisse. [Pliny I.24]
Tu modo enitere ut tibi ipse sis tanti quanti videberis aliis si tibi fueris. [Pliny I.3]