Resin acids usually refers to mixtures primarily. Abietic acid

Abietic acid

Abietic acid , an organic compound that occurs widely in trees. It is the primary component of resin acid, is the primary irritant in pine wood and resin, isolated from rosin and is the most abundant of several closely related organic acids that constitute most of rosin, the solid portion of the...

 is the main component but several related carboxylic acid

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

s. Nearly all resin acids have the same basic skeleton: three fused ring fused with the empirical formula C₁₉H₂₉COOH. These materials occur in rosin

Rosin

.Rosin, also called colophony or Greek pitch , is a solid form of resin obtained from pines and some other plants, mostly conifers, produced by heating fresh liquid resin to vaporize the volatile liquid terpene components. It is semi-transparent and varies in color from yellow to black...

 but also occur in fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 or copal

Copal

Copal is a name given to tree resin that is particularly identified with the aromatic resins used by the cultures of pre-Columbian Mesoamerica as ceremonially burned incense and other purposes...

 resins, in old pine tree stumps, etc. Resin acids are tacky, yellowish gums that are water-insoluble.