Question: Assalamu ‘alaykum,
Some fountain pens incorporate the likes of gold, silver and platinum in their designs (for example, a pen nib may have gold plating). Does the Maliki madhab deem such pens permissible to use? Does carrying one invalidate the prayer (e.g. if it is in one’s pocket)?
Answer: Wa alaykum as salam wa rahmatullah,
According to the Maliki madhab, only solid gold is what would be prohibited when it comes to utensils (cups, plates, pens, boxes, etc). If it is plated, then it would be disliked (makruh) according to the stronger of the two opinions. The other opinion states that it would be haram.
[Section of the Pure in the Abridgment of Khalil]
Rami Nsour
Source:http://seekershub.org/ans-blog/2015/05/07/are-gold-silver-and-platinum-permissible-in-a-pen-maliki-school/