Though superficially similar to neighbouring islands, much of Silhouette is made up of younger syenite dated from 63 million years ago.

[1] The crew of an English East India Company vessel, the Ascension, were the first humans known to step ashore on Silhouette, in 1609.

Also, there is a legend in the Seychelles that the corsair Jean-François Hodoul buried his treasure on Silhouette Island.

There is a mausoleum built in the style of La Madeleine in Paris, Église de la Madeleine, where a number of the family members are buried, including Auguste Dauban, whose business ventures were so extensive he earned the nickname "the Rothschild of the Indian Ocean".

Silhouette Island is one of the richest biodiversity points in the western Indian Ocean with many endemic and threatened plant and animal species.

One of the rarest of these is the Critically Endangered Impatiens gordonii, a white-flowered relative of the well-known garden plant Busy Lizzie, only ever recorded on Mahe and Silhouette.