Chapter 4 – The Aspects (page 26):
SEXTILE (60 degrees angle between 2 planets): The classical astrology meaning of a sextile is that the powers involved cooperate smoothly, so that they encourage and inspire one another. So, both sides of the sextile gain by the aspect between them. This mutual stimulation is usually very creative, on a daily basis. The sextile can be regarded as sort of a lesser trine. Where the latter signifies a kind of harmony that does not necessarily lead to concrete results but is present and helpful anyway, the sextile is often evident and leads to intensified activity as well as palpable results. It is the weakest of the five major aspects (conjunction, opposition, trine, square, and sextile), but it still enhances the planets involved somewhat, compared to what their importance would be without that aspect. The closer the sextile is to 60°, the stronger the aspect is, and the more it enhances the planets involved. In some cases, there can be three or more planets or other points in a sextile, if one or both sides of it has a conjunction. Of course, such a sextile is even more important.