What does Madam Forestier lend Mathilde to wear to the party in "The Necklace" by Guy de Maupassant?

Madame Forestier lends Mathilde a necklace that Mathilde thinks is made of real diamonds but turns out to be costume jewelry.

Mathilde Loisel is upset when her husband says he has an invitation to a fancy ball. She always wishes she had more money and prestige than she does, so he thinks it is a big score. He expects her to be thrilled, but she is upset because she doesn’t think she has the right clothes for the occasion.

She had no clothes, no jewels, nothing. And these were the only things she loved; she felt that she was made for them. She had longed so eagerly to charm, to be desired, to be wildly attractive and sought after.

Her husband gives Mathilde the money he has been saving up to buy a new gun for hunting so she can buy a dress, but she is still unhappy because she doesn’t have a jewel. Her husband suggests flowers are in fashion, but she is not satisfied. He then reminds her that she has a rich friend, Madame Forestier. Mathilde likes this suggestion.

Madame Forestier is willing to lend Mathilde anything she wants. She makes some suggestions, but Mathilde chooses what she thinks is the flashiest and most expensive jewel.  It looks like a diamond.

Suddenly she discovered, in a black satin case, a superb diamond necklace; her heart began to beat covetously. Her hands trembled as she lifted it. She fastened it round her neck, upon her high dress, and remained in ecstasy at sight of herself.

Her friend has no problem lending her the jewel, and is nowhere near as excited about it as Mathilde. Mathilde is the delight of the ball. Everyone looks at her, just as she hoped.  Unfortunately, Mathilde loses the jewel. She and her husband are horrified because they think it is very expensive.

Mathilde and her husband go to a jeweler, who says he did not sell the necklace. After negotiating, they buy a replacement and give it to Madame Forestier without telling her about losing the first one. It takes them years to pay it off. Just when they pay it off, Mathilde learns the necklace she lost was fake.