O icone de mapa não aparece na aplicação.

O android reconheceu o meu icone mapa no canto esquerdo da tela xml, mas ele não está aparecendo na aplicaçao. O que aparece são os 3 pontinhos padrão do menu android.

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context="br.com.rodrigo.agendinha.ListaAlunosActivity">
    <item
        android:id="@+id/menu_enviar_notas"
        android:title="Enviar notas"
        android:icon="@mipmap/ic_enviar"
        app:showAsAction="always" />
    <item
        android:id="@+id/menu_baixar_provas"
        android:title="Baixar provas"
        android:icon="@mipmap/ic_download"
        app:showAsAction="always"/>

    <item
        android:id="@+id/menu_mapa"
        android:title="Visualizar mapa"
        android:icon="@mipmap/ic_mapa1"
        android:showAsAction="always"/>
</menu>

//Lista AlunosActivity

package br.com.rodrigo.agendinha;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.provider.Browser;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;

import java.util.List;

import br.com.rodrigo.agendinha.adapter.AlunosAdapter;
import br.com.rodrigo.agendinha.converter.AlunoConverter;
import br.com.rodrigo.agendinha.dao.AlunoDAO;
import br.com.rodrigo.agendinha.modelo.Aluno;

public class ListaAlunosActivity extends AppCompatActivity {

    private ListView listaAlunos;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_lista_alunos);

        listaAlunos = (ListView) findViewById(R.id.lista_alunos);

        listaAlunos.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> lista, View item, int i, long l) {
                Aluno aluno = (Aluno) listaAlunos.getItemAtPosition(i);
                Intent intentVaiProFormulario = new Intent(ListaAlunosActivity.this, FormularioActivity.class);
                intentVaiProFormulario.putExtra("aluno", aluno);
                startActivity(intentVaiProFormulario);
            }
        });

        Button novoAluno = (Button) findViewById(R.id.novo_aluno);
        novoAluno.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intentVaiProFormulario = new Intent(ListaAlunosActivity.this, FormularioActivity.class);
                startActivity(intentVaiProFormulario);
            }
        });

        registerForContextMenu(listaAlunos);
    }

    private void carregaLista() {
        AlunoDAO dao = new AlunoDAO(this);
        List<Aluno> alunos = dao.buscaAlunos();
        dao.close();


        AlunosAdapter adapter = new AlunosAdapter(this, alunos);
        listaAlunos.setAdapter(adapter);
    }

    @Override
    protected void onResume() {
        super.onResume();
        carregaLista();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_lista_alunos, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.menu_enviar_notas:
                new EnviaAlunosTask(this).execute();
                break;
            case R.id.menu_baixar_provas:
                Intent vaiParaProvas = new Intent(this, ProvasActivity.class);
                startActivity(vaiParaProvas);
                break;
            case R.id.menu_mapa:
                Intent vaiParaMapa = new Intent(this, MapsActivity.class);
                startActivity(vaiParaMapa);
                break;


        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, final ContextMenu.ContextMenuInfo menuInfo) {

        AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) menuInfo;
        final Aluno aluno = (Aluno) listaAlunos.getItemAtPosition(info.position);

        MenuItem itemLigar = menu.add("Ligar");
        itemLigar.setOnMenuItemClickListener(new MenuItem.OnMenuItemClickListener() {
            @Override
            public boolean onMenuItemClick(MenuItem menuItem) {
                if (ActivityCompat.checkSelfPermission(ListaAlunosActivity.this, Manifest.permission.CALL_PHONE)
                        != PackageManager.PERMISSION_GRANTED) {
                    ActivityCompat.requestPermissions(ListaAlunosActivity.this,
                            new String[]{Manifest.permission.CALL_PHONE}, 123);
                } else {
                    Intent intentLigar = new Intent(Intent.ACTION_CALL);
                    intentLigar.setData(Uri.parse("tel:" + aluno.getTelefone()));
                    startActivity(intentLigar);
            }
                return false;
            }
        });

        MenuItem itemSMS = menu.add("Enviar SMS");
        Intent intentSMS = new Intent(Intent.ACTION_VIEW);
        intentSMS.setData(Uri.parse("sms:" + aluno.getTelefone()));
        itemSMS.setIntent(intentSMS);

        MenuItem itemMapa = menu.add("Visualizar no mapa");
        Intent intentMapa = new Intent(Intent.ACTION_VIEW);
        intentMapa.setData(Uri.parse("geo:0,0?q=" + aluno.getEndereco() ));
        itemMapa.setIntent(intentMapa);

        MenuItem itemSite = menu.add("Visitar site");
        Intent intentSite = new Intent(Intent.ACTION_VIEW);

        String site = aluno.getSite();
        if (!site.startsWith("http://")){
            site = "http://" + site;
        }

        intentSite.setData(Uri.parse(site));
        itemSite.setIntent(intentSite);

        MenuItem deletar = menu.add("Deletar");
        deletar.setOnMenuItemClickListener(new MenuItem.OnMenuItemClickListener() {
            @Override
            public boolean onMenuItemClick(MenuItem menuItem) {

                AlunoDAO dao = new AlunoDAO(ListaAlunosActivity.this);
                dao.deleta(aluno);
                dao.close();

                carregaLista();
                return false;
            }
        });
    }
}