What are squares, rectangles, trigons, and parallel grooves classified as?

Squares, rectangles, trigons, and parallel grooves are classified as types of growth marks. Growth marks refer to the distinct patterns or features that occur on a diamond's surface or within the crystal structure as it forms over time. These marks can result from various natural processes during the diamond's growth in the Earth's mantle. Recognizing growth marks is important for gemologists as they can provide valuable information about the history and formation of the diamond.

While types of diamond cuts, inclusions, and shapes are all relevant concepts within diamond grading and identification, they do not encompass the growth marks described in the question. Cuts are related to how a diamond is shaped and refined for aesthetic purposes, inclusions refer to internal flaws that can affect a diamond's clarity, and shapes are the general geometric outlines a diamond can take after cutting. Thus, the classification of squares, rectangles, trigons, and parallel grooves aligns specifically with growth marks, indicating their origins in the natural formation process of diamonds.