Wall of Marble

This is a proprietary spell of Chrailis and is a closely guarded secret. It has a version that all spellcasters can use at 5th level. The spell is only handed out by Coterie Gorahz, usually only to those of Aristocrat rank.   Any granted the spell are given strict instructions not to share the spell with others.
It has two versions. The first conforms exactly to Wall of Stone except the stone created is marble. This marble can be used as a covering for other stones and melded into the attached stone just as the normal spell would. 
The second version converts an area of regular stone to marble. The area of effect for the second version is double that of the normal spell.
The marble created by either spell is white with veining of whatever color the caster desires. 
The marble, while not magical, is harder than regular marble, resistant to regular steel (not iron), and more acid-resistant.

This item was Chad's 2019 Birthday Present.
The story associated with it is:

Oops, Morvion might be in trouble with City Planning. He’s creating a tower made of common stone a little too near Chrailis. Per law, all towers must be made with a mainly white Marble to conform with the rest of the city. The notice spiked into the wall of his tower said to expect it to be demolished within three days. His immediate solutions was to not build over 2 stories, of which any stone or wood is allowed. His second solution is to build his tower another 10 miles away from the city, far enough out that it wouldn’t be seen as part of the city.
Beneath the first notice was a small leather pouch held by a second spike. In it are two scrolls, small scroll with a message and a second scroll with a new spell.
The note in the second scroll reads as follows: “Greetings, For service to Chrailis, the desctruction of your tower will be delayed by two weeks, allowing you time to conform to building standards. In the meantime, this spell is being granted to you. It is a restricted spell taught to few. DO NOT let others learn this spell – Sister Moleoska” It is signed with a Coterie house symbol of Coterie Gorahz.