Recently, a newly raised Brother read about a chisel being a symbol in Freemasonry but did not recall it being mentioned as a working tool in the degrees.  He questioned if there is a Masonic significance.  Though it is not utilized in the Pennsylvania Degrees, here is the answer:

Chisel.  In the American Rite the chisel is one of the working tools of a Marked Master and symbolizes the effects of education on the human mind.  For as the artist, by the aid of this instrument, gives form and regularity to the shapeless mass of stone, so education, by cultivating the ideas and by polishing the rude thoughts, transforms the ignorant savage into the civilized being.

In the English ritual, the chisel is one of the working tools of the Entered Apprentice.  With the same reference to the advantages of education.  Preston (B.II., Sect. vi) thus elaborates its symbolism as one of the implements of Masonry: “The chisel demonstrates the advantages of discipline and education.  The mind, like the diamond in its original state, is unpolished; but as the effects of the chisel on the external coat soon present to view the latent beauties of the diamond, so education discovers the latent virtues of the mind and draws them forth to range the large field of matter and space, in order to display the summit of human knowledge, our duty to God and to man.”  (Illustrations, ed. 1812, p. 86, footnote.)  But the idea is not original with Preston.  It is found in Hutchinson, who, however, does not claim it as his own.  It formed, most probably, a portion of the lectures of the period.  In the French system, the chisel is placed on the tracing board of the Fellow-Craft as an implement with which to work upon and polish the Rough Ashlar.  It has, therefore, there the same symbolic signification.

An Encyclopedia of Freemasonry and Its Kindred Sciences by Albert G. Mackey