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Andradite is a garnet, and you may wish to familiarise yourself with the garnet group before reading this. Garnets are miscible with each other, and a given specimen may thus be an intermediate between two or more species, and thus have intermediate properties. Andradite occurs in a number of interesting deposits, even if they do not produce collectible specimens. Some of these include so-called skarn rocks, more or less massive silicates associating iron- and manganese-ores. In these the Andradite will be massive, granular, and often be matrix for otherwise rare and unusual minerals. Famous skarn deposits include Långban, Jakobsberg, and Harstigen in Sweden, where rare and unusual minerals occur in the skarns. These deposits carry an Andradite variety, Rothoffite, that has a high manganese content, but note that only very little of the Andradite qualifies as Rothoffite, most is just plain Andradite with a trace of manganese. Rothoffite is an Andradite with app. 20% Calderite (the Mn-Fe-garnet).
Reasonably pure Andradite is often greenish yellow or brownish, and collectible specimens often come from carbonatites or schists. Andradite varieties include the golden Topazolite and the green Demantoid, both of which are cherished gems if transparent. Both are moderately rare as gems, mostly found as individual stones or in small lots, though substantial amounts of a greyish green Demantoid were produced in Namibia in the second half of the 1990s, and a few lots of very clean, saturated green (say 'Emerald green' for the lack of a better term) Demantoid came out of Russia in the same period.
Melanite is a black variety of Andradite, owing its colour to titanium, and it is an intermediate between pure Andradite and Schorlomite. It can produce quite appealing specimens of lustrous black crystals.
My records indicate that Andradite from a range of deposits occurs on specimens that also carry one or more of the following minerals: Actinolite, €girine var. Ferro- schefferite, €girine var. Schefferite, Antigorite, Aragonite, Bergslagite, Biotite var. Manganophyllite, Braunite, Calcite, Chalcopyrite, Chrysotile, Clinochlore, Copper, Cymrite, Diopside, Dolomite, Epidote, Fluorapatite, Fluorite, Franklinite, Galena, Gaudefroyite, Hancockite, Hausmannite, Hedenbergite, Hematite, Hendricksite, Jennite, Johnbaumite, Leucite, Leucophoenicite, Leucophoenicite, Liottite, Långbanite, Magnetite, Manganese-axinite, Margarosanite, Melanotekite, Millerite, Mooreite, Opal, Orthoclase, Perovskite, Pyrite, Quartz, Rauenthalite, Rhodonite, Richterite, Sanidine, Scheelite, Sphalerite, Titanite, Vesuvianite, Willemite, and Zincite.