The Protagonist of 'The Baroque Marble' is Sister Opal.
A protagonist is known as the main character of the story and in this case it is Sister Opal because the story centers on this character. In most cases the author will present the protagonist with a goal that they will aim to reach by the end of the story, however there will generally be obstacles that are thrown in along the way. These obstacles can be shown in different ways for example, they can be a natural disaster or there can be human obstacles that are known as antagonists. The other characters introduced in the story are commonly referred to as minor characters. Their places in the story can be either to help the protagonist reach their goal or they may be implemented to help preventing it from happening. You should also keep in mind that there can be more than one protagonist in a story. When a female protagonist is used in a story, there are a number of ways that they can be introduced to indicate that she is the main character. For example, with regards to a short story, the female protagonist will tend to be introduced in the first paragraph or the first sentence. One particular physical attribute of the female character will tend to be described in more detail in order to set them apart from any other female characters in the story. Moreover, her clothing will be described in more detail as well as her surroundings so the reader can create the image in their mind.