Wall mirrors reflect light in a space and are a desirable decorative element in design, and one place a chic wall mirror is always at home is when it's hung above a mantel.
A shapely mirror hung above a mantel helps to balance the weight of a firebox that traditionally sits closer to the floor and the combination of the two creates a dramatic focal point.
The four spaces you'll most often find a fireplace are the living room, family room, formal dining room, and master bedroom, yet any space with a fireplace and mantel provides an opportunity to hang unique or decorative wall mirrors.
A round mirror with its circular shape will balance the angles of a square fireplace. Group a round mirror and a collection of framed works of art (illustrations, paintings, or prints) above a mantel for a timeless display that looks attractive in any season.
A rectangular mirror stretches higher toward the ceiling to fill the vertical space, choose one that complements the style of your home, an ornate gilded form is a traditional choice, but modern shapes that draw the eye to their frames are available too. 
There's no rule that dictates which shape a mirror above a mantel should take, choosing one that is arched or shapely adds allure to a mantel with its flowing lines or protruding detail. 
Nine options for mantel top mirrors appear from top left to bottom right below:
Round
1) take advantage of the clean lines of the simple Harrin Maple wood mirror, 2) bring a layer of texture with the spiraled petals of the flower jute wall mirror, or 3) add glamour with the modern shape of the geometric faceted Sorrento gold mirror.
Rectangular
4) Intricate squares are an attractive border on the Greek key inspired gold leaf Devoll mirror, 5) add organic appeal with the wood border rustic wall mirror, or 6) embrace the gray trend with the bone inlay Abscissa chevron mirror.
Shapely
7) Ebony bone inlay and a curvy top detail make the Vicario wall mirror a true conversation piece, 8) the shapely Arzana bone inlay with its twisted loops is a sophisticated choice, while the 9) beautiful beveled bronze openwork mirror will capture anyone's attention. 
Find many more ideas for decorative or shapely wall mirror placement in the Lamps Plus Shop by Room galleries!
Image sources: my domaine, rue magazine, the inspired room