When Mathilde first comes across the diamond necklace, the story uses a metaphor to vividly convey the excitement she feels:
All at once, in a black satin box, Madame Loisel unearthed a superb diamond necklace, and her heart began pounding with unrestrained desire.
In this scene, Mathilde metaphorically “unearth[s]” the story’s clearest symbol of wealth and status: the necklace. It is clear from the very beginning that Mathilde has always seen herself as entitled to a luxurious life. She has “suffered endlessly” for her lack of “all delicacies and all luxuries,” and she often thinks about how her life falls short of her decadent fantasies. The verb “unearthed” implies a rigorous and long search for the object in question, as if Mathilde has spent her whole life looking for the kind of status she thinks she has now found in Jeanne’s jewelry box.
In keeping with her feelings about wealth and status, Mathilde has a strong physical reaction to the necklace, as her heart starts "pounding." Her "unrestrained desire" drives her to want what appears to be the most expensive piece of jewelry that Jeanne owns, and finding it makes her feel like she has come across some sort of buried treasure—something, it seems, that has the power to change her entire life.
