Soon we will start a campaign in Eberron with a magician in the group, this magician is very interested in arcane relics from which he can learn and for his magic objects a Spellshard that in turn was an Arcane Grimoire would not be bad. 

We really don't know if a Spellshard is completely the same as a book, in the sense that it could be another similar magical object like tomes.

I'm guessing by magician, you mean wizard, since they're the only ones that use spellbooks (which is what I assume you mean by arcane grimoire). The description for a spellshard specifically says it can be used as a spellbook, and explains how it is used. It also says that a spellshard is a dragonshard, which is basically a magic rock. It doesn't open like a book, instead "While holding the shard, you can use an action to open your mind to the shard, seeing its content in your mind. "

Does that clear it up?

In addition to Xalthu’s comment, I’d like to add a comment and a “correction.”

First, the comment:

Even a “traditional Spellbook” doesn’t actually have to be a “spell book” per se. From the Wizard’s specific Spellcasting feature:

The Book’s Appearance. Your spellbook is a unique compilation of spells, with its own decorative flourishes and margin notes. It might be a plain, functional leather volume that you received as a gift from your master, a finely bound gilt-edged tome you found in an ancient library, or even a loose collection of notes scrounged together after you lost your previous spellbook in a mishap.

I once played with someone who decided their Spellbook was a binder full of "Magic cards," (as in M:tG) later someone else decided theirs was a deck of cards and they flavored their Wiz as pulling strands of mana and drawing & playing cards from the deck to cast. Someone else once used a collection of scrolls (not spell scrolls), great big scrolls like the Torah. Someone else flavored theirs like Cortana from Halo, another person decided theirs was like the handheld device Al used to communicate with Ziggy on Quantum Leap. (D&D used to have crashed spaceships in it and everything.) Another person's was a massive stone tablet with itty itty engravings for the writing, and another fancied themselves after Druids, so they used to collect pieces of birch bark to use as their Spellbook. (I was “that guy” once and used pockets full of cocktail napkins. 🤷‍♂️ It was 10th grade, whadaya want?)

However, that’s all just “flavoring” for the aesthetic. Actual RAW specifically states:

Spellshard

This polished Eberron dragonshard fits in the hand and stores information similar to a book. The shard can hold the equivalent of one book that’s no more than 320 pages long….

[Sic]

A wizard can use a spellshard as a spellbook, with the usual cost in gold and time to “scribe” a spell into the shard.

Now the correction:

Wizards aren’t the only ones to use a book of spells. Besides the Ritual Caster feat, a Warlock who takes the Pact of the Tome pact boon gets a “Grimoire” known as their “Book of Shadows.” The description for the Spellshard explicitly mentions a Wiz using a Spellshard as a Spellbook, but never mentions anything about a Warlock using one as their BoS. That’s not actually RAW, but if the DM decided it was RAF, then they are free to rule that a Warlock could use one.

Thank you very much, the truth was something that "we would do anyway", but I wanted to know if there were any mechanics related to that.