Some jewelry sellers dwscribe the gem stone as sapphire solitaire. It seems to be not a real sapphire. But what kind of stone is it
Thanks

There can be real sapphire solitaires and there can be fake sapphire solitaires.

https://www.google.com/search?q=sapphire+solitaire&rlz=1C9BKJA_enUS699US700&oq=sapphire+soli&aqs=chrome.1.69i57j0l3j69i60.7421j0j8&hl=en-US&sourceid=chrome-mobile&ie=UTF-8

There's really no way to know what the stone is without seeing it, and without being a gem expert. You won't find an answer to this question online.

Well solitair means 'alone', so it has been mounted without embellishment. There are two or three types of saphires; one is 'star' saphire, which has an image of a star at its centre. This is the most sought after. A plain saphire is not worth a heck of a lot, but you will have to take it to a gemologist at a jewellery store to have it appraised.